This will let you modify tags:

Applescript:

use AppleScript version "2.3.1"
use scripting additions
use framework "Foundation"

on returnTagsFor:posixPath -- get the tags
   set aURL to current application's |NSURL|'s fileURLWithPath:posixPath -- make URL
   set {theResult, theTags} to aURL's getResourceValue:(reference) forKey:(current application's NSURLTagNamesKey) |error|:(missing value)
   if theTags = missing value then return {} -- because when there are none, it returns missing value
   return theTags as list
end returnTagsFor:

on setTags:tagList forPath:posixPath -- set the tags, replacing any existing
   set aURL to current application's |NSURL|'s fileURLWithPath:posixPath -- make URL
   aURL's setResourceValue:tagList forKey:(current application's NSURLTagNamesKey) |error|:(missing value)
end setTags:forPath:

on addTags:tagList forPath:posixPath -- add to existing tags
   set aURL to current application's |NSURL|'s fileURLWithPath:posixPath -- make URL
   -- get existing tags
   set {theResult, theTags} to aURL's getResourceValue:(reference) forKey:(current application's NSURLTagNamesKey) |error|:(missing value)
   if theTags ≠ missing value then -- add new tags
       set tagList to (theTags as list) & tagList
       set tagList to (current application's NSOrderedSet's orderedSetWithArray:tagList)'s allObjects() -- delete any duplicates
   end if
   aURL's setResourceValue:tagList forKey:(current application's NSURLTagNamesKey) |error|:(missing value)
end addTags:forPath:

set theFile to POSIX path of (choose file)

its returnTagsFor:theFile

Your code is only assigning a tag indirectly. It's actually (re-)assigning the Finder label (kMDItemFSLabel), which these days is arguably only there for backwards compatibility; the system adds a (roughly) matching tag at the same time.

Have you pulled that script out of your archives? Because I don't think those colors match what you actually see these days (the names of which are localized, I believe).

Yes, I mis-spoke -- it's just the order they appear in the UI that's changed.

As I am curious, I tried the given script using a list of localized color names.

It's easy to get these names:

Applescript:

set theNames to {}
repeat with i from 0 to 7
   set theKey to ("TG_COLOR_" & i)
   tell application "Finder" to set theName to localized string theKey
   set end of theNames to {theKey, theName}
end repeat
theNames
--> {{"TG_COLOR_0", "Aucune couleur"}, {"TG_COLOR_1", "Gris"}, {"TG_COLOR_2", "Vert"}, {"TG_COLOR_3", "Violet"}, {"TG_COLOR_4", "Bleu"}, {"TG_COLOR_5", "Jaune"}, {"TG_COLOR_6", "Rouge"}, {"TG_COLOR_7", "Orange"}}

I edited the choose from list instruction as :

Applescript:

set tagList to choose from list {"Rouge", "Orange", "Jaune", "Vert", "Bleu", "Gris", "Violet"} with title "Tag Selected Items" with prompt "Choose colors:" OK button name "Apply" cancel button name "Cancel" with multiple selections allowed and empty selection allowed

Good point, we may use the English names or the localized ones, the behavior will be the same.

Yvan KOENIG running High Sierra 10.13.6 in French (VALLAURIS, France) mardi 14 mai 2019  18:35:11

The keys used to localize strings aren't defined in the sdefs.
We may just get them in the resources files available in application's bundles.
TG_COLOR_x where x is a digit from 0 to 7 is a key in the localizable.strings files used by the system to localize some strings. It's the one reachable by default but there are numerous other ones.
For French resources they are in the folder:
"/System/Library/CoreServices/Finder.app/Contents/Resources/French.lproj/"
The complete list is :
AboutWindow.strings
AirDropCollectionView.strings
AirDropDiscoverableModePopoverView.strings
AirDropIconView.strings
AirDropInfoView.strings
AirDropLegacyModePopoverView.strings
AirDropNotAvailableView.strings
ArrangeByMenu.strings
BannerView.strings
BulkRenameWindow.strings
ClipWindow.strings
ColumnCellView.strings
ColumnPreview.strings
ColumnView.strings
DecryptionPasswordSheet.strings
FFKBrowserWindow.strings
FFKMenuBar.strings
GotoWindow.strings
GroupNameField.strings
ICloudNoDocumentsView.strings
iCloudQuotaBanner.strings
ICloudSetupView.strings
ICloudUpgradeView.strings
IconCollectionGroupHeaderView.strings
InfoPlist.strings
ListView.strings
Localizable.strings
NavChooseApp.strings
PreferencesWindow.strings
ProgressErrorView.strings
ProgressStatusView.strings
ProgressStatusView2Line.strings
SearchCriteriaSheet.strings
SearchForSlice.strings
SearchScopeSlice.strings
ServicesMenu.strings
SidebarView.strings
SimpleGrouping.strings
SlicesAttributeNameOverrides.strings
SlicesStrings.strings
StatusBar.strings
TagColumnTableView.strings
TagsPrefCellView.strings
Toolbar.strings
ViewOptionsWindow.strings

Infos about these resources are given in Standard Additions's dictionary:

localized string v : Return the localized string for the specified key
localized string text : the key
[from table text] : the name of the strings file excluding the “.strings” suffix (default is “Localizable”)
[in bundle file] : an alias or file reference to the bundle containing the strings file (default is the current application/script bundle)
→ text : the localized string

Example with the results returned under a system running in French.
CAUTION: The keys aren't guaranteed to survive a major version change.

Applescript:

(*
Simple case, the string to localize is defined in the table Localizable.strings.
There is no need to describe explicitely the table and the source bundle.
*)

tell application "Finder" to set toRemoveFromiCloudDrive_loc to localized string "A31"
--> "Pour supprimer des éléments d’iCloud Drive, déplacez-les dans votre dossier Bureau ou Documents sur ce Mac."

(*
If the string is defined in an other file we must pass the table's name (without the suffix .strings) and the bundle stroring it
*)
set FinderBundle to path to application "Finder"
--> alias "SSD 500:System:Library:CoreServices:Finder.app:"
set IconSize_loc to localized string "383.title" from table "ViewOptionsWindow" in bundle FinderBundle
--> "Taille des icônes :"

set |Finder/Reveal_loc| to localized string "Finder/Reveal" from table "ServicesMenu" in bundle FinderBundle
--> "Finder/Afficher dans le Finder"

set LastOpen_loc to localized string "116.title" from table "ArrangeByMenu" in bundle FinderBundle
--> "Date de dernière ouverture"

# Other one for the fun

set Volume_loc to localized string "tCs-xJ-UEw.title" from table "ArrangeByMenu" in bundle FinderBundle
--> "Volume"

# It seems that there is no global control upon these tables so several keys may describe the same string.
set showLibrary_loc1 to localized string "Ukt-Pm-iTw.title" from table "ViewOptionsWindow" in bundle FinderBundle
--> "Afficher le dossier Bibliothèque"
set showLibrary_loc2 to localized string "noX-Qe-gkU.title" from table "ViewOptionsWindow" in bundle FinderBundle
--> "Afficher le dossier Bibliothèque"
set showLibrary_loc3 to localized string "sld-Oo-X54.title" from table "ViewOptionsWindow" in bundle FinderBundle
--> "Afficher le dossier Bibliothèque"

I use localized string for years and met changes only two or three times.

Yvan KOENIG running High Sierra 10.13.6 in French (VALLAURIS, France) mercredi 15 mai 2019  12:08:55

Last edited by Yvan Koenig (2019-05-15 04:15:44 am)

I'm back about localized string because I forgot an important feature.
Sometimes, the English.lproj doesn't contain every tables available for other countries.
You will see some examples below.
You will discover a case where I am unable to find the correct English spelling.

Applescript:

(*
Simple case, the string to localize is defined in the table Localizable.strings.
There is no need to describe explicitely the table and the source bundle.
*)

tell application "Finder" to set toRemoveFromiCloudDrive_loc to localized string "A31"
--> "Pour supprimer des éléments d’iCloud Drive, déplacez-les dans votre dossier Bureau ou Documents sur ce Mac."

(*
If the string is defined in an other file we must pass the table's name (without the suffix .strings) and the bundle stroring it
*)
set FinderBundle to path to application "Finder"
--> alias "SSD 500:System:Library:CoreServices:Finder.app:"

set theKey to "383.title"
set IconSize_loc to localized string theKey from table "ViewOptionsWindow" in bundle FinderBundle
if IconSize_loc = theKey then # The system run in English for which there is no table "ViewOptionsWindow"
   set IconSize_loc to "Icon size:"
end if
log IconSize_loc --> "Taille des icônes :"

set |Finder/Reveal_loc| to localized string "Finder/Reveal" from table "ServicesMenu" in bundle FinderBundle
--> "Finder/Afficher dans le Finder"

set theKey to "116.title"
set LastOpen_loc to localized string theKey from table "ArrangeByMenu" in bundle FinderBundle
if LastOpen_loc = theKey then # The system run in English for which there is no table "ArrangeByMenu"
   set LastOpen_loc to "Date Last Opened"
end if
log LastOpen_loc --> "Date de dernière ouverture"

# Other one for the fun
set theKey to "tCs-xJ-UEw.title"
set Volume_loc to localized string theKey from table "ArrangeByMenu" in bundle FinderBundle
if Volume_loc = theKey then # The system run in English for which there is no table "ArrangeByMenu"
   set Volume_loc to "Volume"
   (*
In fact I don't know which is the exact spelling.
in Russian it's "по тому" which according to Google means "on that"
in Spanish it's "Volumen" which according to Google means "Volume"
in Japanese it's "ボリューム" which according to Google means "Volume"
And I never saw this string in the View menu which contain the ArrangeBy menu
*)
end if
log Volume_loc --> "Volume"

# It seems that there is no global control upon these tables so several keys may describe the same string.
set theKey to "Ukt-Pm-iTw.title"
set showLibrary_loc1 to localized string theKey from table "ViewOptionsWindow" in bundle FinderBundle
if showLibrary_loc1 = theKey then # The system run in English for which there is no table "ViewOptionsWindow"
   set showLibrary_loc1 to "Show Library Folder"
end if
log showLibrary_loc1 -->"Afficher le dossier Bibliothèque"

set theKey to "noX-Qe-gkU.title"
set showLibrary_loc2 to localized string theKey from table "ViewOptionsWindow" in bundle FinderBundle
if showLibrary_loc2 = theKey then # The system run in English for which there is no table "ViewOptionsWindow"
   set showLibrary_loc2 to "Show Library Folder"
end if
log showLibrary_loc2 -->"Afficher le dossier Bibliothèque"

set theKey to "sld-Oo-X54.title"
set showLibrary_loc3 to localized string theKey from table "ViewOptionsWindow" in bundle FinderBundle
if showLibrary_loc3 = theKey then # The system run in English for which there is no table "ViewOptionsWindow"
   set showLibrary_loc3 to "Show Library Folder"
end if
log showLibrary_loc3 -->"Afficher le dossier Bibliothèque"

Happily, such annoying cases are rare.

Yvan KOENIG running High Sierra 10.13.6 in French (VALLAURIS, France) jeudi 16 mai 2019  12:38:15

Thanks Shane.
What you wrote may explain why several keys may be used to describe the same string.
As I am curious, I ran my sample script upon Finder 10.12.6 and - I am lucky - the "easy to remember keys" available in Finder 10.13.6 were already available in the old version.

In practice it's not really important. I never had to use such keys. I use localized string when I have to write GUI scripting code where the name of UI elements are always localized.
The fact that some tables are unavailable in English.lprog is more annoying.
I'm wondering were are the English strings defined in such cases.

I'm really puzzled by the key "tCs-xJ-UEw.title" in the table ArrangeByMenu.strings.
Most of the time the local string means volume but sometimes it's really different.
For instance, the danish key is Enhed which is supposed to mean Unit.

And of course I'm always unable to find where is this string really used.

Yvan KOENIG running High Sierra 10.13.6 in French (VALLAURIS, France) vendredi 17 mai 2019  12:08:03