[Koha] Authorities localization?

[Joel Cornuz]

Hello Everyone

My name is Joel Cornuz, I am the IT manager for a small school in 
Montreal using (with success!!!) Koha for its library (15k volumes). 
Many thanks for this great tool that is giving us access to a world 
class library system!!!

I asked that same question on the devel mailling list and was told I 
would have better chance to get help here, so here it is:

Our books are a mix of French and English volumes and we would like to 
translate our authorities (the topical terms). The idea is that we want 
our students to have access to topical terms in French or in English, 
and access to our complete collection (French and English volumes) 
related to this particular topic.

I know that it is possible to duplicate an authority - so one idea was 
to duplicate (and translate) authorities... but then I didn't find a 
simple way to automatically link items from the source to the 
duplicated authority (am I missing something there?)

Or is there a way to localize existing authorities? 

Or is there another (different, better) way?

Many thanks for your help.

Joel