I have multiple Q2A sites with different languages, the user_db is the same for all, the label name gets translated in the various languages, I added the custom filed nationality and tried to figure out how the standard labels get their value out of the language file...
but somewhere down the line I got too confused tracing the code, in th db its pretty simple, i set the content to null and hoped Q2A would automatically pick up my added label in the langauge files...