Although I have language values for French, german, Italian, Spanish and now Ukraine in my app, French users are reporting that the app no longer presents in French.
This is a relatively recent thing
Whats changed at my end:
Switched to App Wrapper 4
Switched to Big Sur
Added Ukranian language defs
When I go to my system prefs, add French and make it top of the language list, the app works in French for me.
What can I check?
My customers complaining about this may have this language order wrong.
For example they may only have Dutch selected and macOS shows them German instead of English.
Solution is to add English on their list as second choice.
Interesting. I ought to add that the build language is English, which is why I didnt mention it.
They are French and they get English.
Big Sur introduced a new system setting to set the language of an app, maybe this might help your users (if they are already on Big Sur).
Otherwise there are two or three small apps which change the default language of an app in older macOS systems. You can search für “LanguageSwitcher”, one of those is mine (https://www.deltaworx.de/download/Language_Switcher.dmg) 
If they are fine with using the terminal, they can use the “defaults write …” command to set the language without the need of any app.
The process you describe is known to me.
It seems that in this situation, you cannot go to Preferences and force an app to use French while your machine is set to French.
I’ll recommend your app to the client and see how they fare. (since it all works fine for ME, as you would expect) … thanks.
Did you have a look at the one of the users computers yourself?
Not yet.
Another guess… did you test with the App wrapped by AW4 or with the “unwrapped” version? I am asking because AW4 has a new option to automatically remove partial translated languages…
Yup.
I know about that. AW3 had some similar function.
Its all set properly in AW4
The language files still exist in the app contents.
I can force French by deleting the en.lproj file.
Its just not seeming to detect the French environment
Just curious… what happens if you set the language to Default in the build settings?
Thats likely to be it Greg.
I checked and at some point it has changed to English (UK)
I’ll build and try it now.
(I think this happened as a side effect of importing the Ukranian language file: its been working for years without me ever looking at that particular screen in the IDE)