I prefer to have 1 language/VB, so then...
- VB won't become too big as a file like others has said before me in this threat
- UGHT, OTO GONNA BE A BIG WORK (and recording very likely too)
- no need to scratch own head and be like "hmm how gonna I name two different R's or E's" for example (unless you know X-sampa - or you're creative enough for own naming system?)
- The accent... It's impossible to make a multi language VB to have an "native" accent for each language (my accent and pitch changes between my two mother languages). You would need to choose "main support language" + "accent".
- The languages; if absolutely wanna make a multilingual VB, it's good idea that the languages' phonetics aren't /too/ far away each other. Like
@danlof99 mentioned: Spanish and Japanese will still be workable due similar vowels/consonants (basically need to two different "u" for Japanese/Spanish and add some ending consonants and CC for Spanish) but then other language combinations will be very likely eww and reclist length going to explode
I personally like that 1 language per VB works the best (with some extra samples for example for Engrish or something). It's easiest in that way IMO.
Lastly: Very VERY few people actually NEEDS a multi language VB at the end; people (usually) works mainly with one or two language(s) only.