canXYZ() naming maybe implies boolean return values

[domenic]

In addition to the discussions in #7 and #12 about these methods, a simpler problem is that most people expect that a method starting with "can" to return a boolean value.

Maybe if we went in the direction of #7, "can" would still be an OK prefix. But probably we should pick something different, e.g. languageAvailable() / languagePairAvailable().