Add localization support

[urbalazs]

It would be nice that all user-facing strings like output of --help or massages printed during usage can be translatable into other languages. Many users do not speak English.

[joto]

I agree that it would be nice if users could use Osmium in their own language. But Osmium is a niche tool for a small audience and it isn't very likely that we'll get good and up-to-date translations for the texts from the community. It will need some work to add l18n support and then we're likely to end up with very few and incomplete translations. And when changes to the code are made those texts will be outdated quickly. If somebody feels strongly about this and wants to tackle this project, please speak up, otherwise this will not happen.

[urbalazs]

• Current situation: osmium speaks in English.
• Best case: translators provide translations for many languages, and osmium can speak in many languages. Translators maintain their translations.
• Worst case: osmium supports localization, but no one or just a few translators see opportunity to add translations. In a few languages, osmium speaks these languages, but mostly in English.

As I see, the worst case is still better than the current situation. I understand that localization support require some extra effort, but this is just one time task. Adding new strings require no extra effort just add _(...) around the string. Changing existing string does not require this, since encapsulation is already there.

I would like to add Hungarian translation if possible. So one thumbs up from my side.