Set translation fallback to False per default

i18n.translate() is used for L10N whereas i18n translations
are done by i18n.tntranslate. Because L10N is site-dependend and
not language-dependent, fallback must be False per default.
Otherwise the given results (templates, categories etc.) may be
wrong.

Change-Id: I15956db5490dec4ca9f7d55d53eb2ebc1a633790
Merge "Set translation fallback to False per default"