You can see the underlying problem by setting the Metadata > Color Label Set to Lightroom Standard (though you can't assume the other person has done this). First, let's assume LR is working in German, so selecting an image and pressing 9 adds "Blau" (from the LR Standard in German) in the label field and the colour label is displayed as blue. Now set LR's language to English and restart LR - the text "Blau" remains in the label field but the colour label isn't blue because now "blau" doesn't match anything in colorNameForLabel.
Each language's translations are inside the LR application in a file called something like TranslatedStrings_Lr_it_IT.txt etc. So you could programatically import each language and find the text string for the labels.
"$$$/AgLibrary/Menu/Collection/Label/Blue=Blu"
"$$$/AgLibrary/Menu/Collection/Label/Green=Verde"
"$$$/AgLibrary/Menu/Collection/Label/None=Nessuna"
"$$$/AgLibrary/Menu/Collection/Label/Purple=Viola"
"$$$/AgLibrary/Menu/Collection/Label/Red=Rosso"
"$$$/AgLibrary/Menu/Collection/Label/Yellow=Giallo"
But if someone enabled a different Color Label Set when they hit 9 and added a blue label, then 9 could enter "xyz" into the Label field if that waas how the Color Label Set was set up.
I hope I've explained this well. It's complicated, or should that be messy? In a multi-user multi-language environment, t's not very disciplined.