Small update for the dutch translation

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Italian translation: update
Merge pull request #422 from Ansa89/italian-translation

Italian translation: update
Update German translation
Merge pull request #424 from sfan5/master

Update German translation
Merge pull request #420 from Impyy/dutch-update

Small update for the dutch translation
Reuse S and SLEN macros in drawstr macro

A minor step toward decoupling from particular i18n implementation.
Split i18n into separate files per language

This separates different languages into self-contained files,
with strict order-independent ID->STRING correspondence,
automatic fallback to English for untranslated IDs, and
a syntax closely resembling (but not really valid)
gettext's PO files, in case we ever migrate to it.

Also, two new IDs are added for future use:
LANG_NATIVE_NAME for the language name in the language itself,
and LANG_ENGLISH_NAME for the language name in English.
These are expected to be used e.g. in language choice menu.
Eventually.
Stop relying on hardcoded size for i18n tables