Hi Sebas,
I am not actually sure I quite understand the multi-language approach you were trying to take.
Fwiw, for more than one reason, I would not recommend overloading individual tiddlers
with various language versions of it in the form of fields, problem #1 being the title.
Admittedly, I have yet to see a properly defined multi-language operational mode emerge.
To avoid conflicts, I would have all tiddlers prefixed with the language, e.g. en-Welcome, fr-Bienvenue...
and then have that prefix removed from the title display, and display a "pretty-title" if defined in a field.
Ideally, that pretty title (or the title after removing the language prefix) is consistently displayed throughout the wiki,
not just in the title itself but also for links. So, this begs for a core LinkTemplate.
In any case, translations would not be different fields here, but independent tiddlers.
I probably would define a master language of which to make translated versions in other languages.
Each language version would point to the corresponding tiddler in the master language, e.g. in some "master" field.
In other words, all translated versions could be fetched by looking for all tiddlers that have their
master field set to a give title, e.g. to the same title as the one we're looking at...
and could be displayed as of this or that language depending on the prefix.