Safe to remove extra languages?

I have used Monolingual. It's safe, but check the FAQ on the site carefully before you proceed, as there are a few gotchas.

Matt

Unless you are strapped for HD space, there is no reason to remove them. They are not active components. They merely sit there.
Usually when people think about removing 6 GB or so of files, it means that their HD is too small.
It's like having 2 DVDs stored on the HD. Hardly worth thinking about with modern HDs so large and inexpensive.
And, as noted, removing system files can sometimes be problematical.
At the very least be sure TM has backed up the entire OS before removing some components.

This page from TinkerTool System has some info and caveats about language removal.

Unless you are strapped for HD space, there is no reason to remove them.

Actually, there is a very minor benefit even if you have tons of free space: by reducing the number of files in the OS, certain operations (mostly related to utilities) take a bit less time. It isn't because there is less space used but because there are fewer files to go through. Most users just look at the space used by the language files, which isn't particularly significant unless you are indeed very short on drive space, but the sizable file count reduction is probably more significant.

Still, this is a matter of maybe a few seconds saved per day for the typical user & probably isn't worth the effort, especially if a removed file does need to be replaced.