Internationalization of built in messages

[psychoslave]

Messages like "lexical element too long" should be localizable.

This could be made independent from the localization of built in tokens. That is, a built in message referring to "" might let the token untranslated if the platform doesn't use translated tokens.

Indeed, the platform should take into account environment variable, like LANG, to determine the language in which messages should appear. But this should probably not be used regarding autoload of localized version of tokens. For this, it would probably more relevant to rely on explicit statements which load the localized tokens and other possible localized syntactic sugar. Thus said, if localized built in tokens went loaded, then the messages should also reflect this change.