Allow langcode as argument for i18n_taxonomy_localize_terms()

The standard way to have a taxonomy term localized is by using the function i18n_taxonomy_localize_terms().
However, this function does not accept a custom language code for which we want the taxonomy term to be localized, it can only be used for the current language.

Having a langcode as an argument, would give a lot more flexibility to this function.

I will add a patch for this.

Thank you !