Drop load(), loadc(), string() and stringf() from the luci.i18n class since
these functions are either no longer unused or were never used to begin with.
Also slightly rework the module to only use local symbols and unify the
module require style.
Signed-off-by: Jo-Philipp Wich <jo@mein.io>
Rework the setlanguage() implementation to actually switch catalogues
if another language has been loaded previously and change it to return
the effectively loaded language tag.
Also improve input parameter validation and accept tags in both lower
or upper case.
Signed-off-by: Jo-Philipp Wich <jo@mein.io>
