I don't think removing modules that are not in use will do anything to improve performance...not using modules such as chat and quiz could greatly improve performance, but just making them unavailable is the same as removing them as far as performance goes. I don't think the number of languages you have will make a difference on performance one way or another.
Also, removing modules if you also remove their styles will help some (some modules more than others) styles.php can be a huge file with the standard theme and.
There is more discussion of performance improvements with removing langs and mods here.
- enable langcache and/or reduce the number of allowed languages
- use a PHP precompiler
- disable filters
- disable modules
- trim Apache's maxclients, MySQL maxconnections according to your RAM availability (see earlier threads about maxclients)
- maintain your DB indexes
- switch to Postgres ;)