For translation bug reports, the recommended severity to use is wishlist.
The recommended tags are l10n tag as well as the patch tag (because the bug report includes the needed "fix" by including the translation file).
The d-i tag must be used for core D-I translations as well as base-config and tasksel.
The subject of the bug report should start with "[INTL:xx]". When the package has several translatable materials, the subject should mention which translation is sent.
When translators want to send more than one translation file, they should send one bug report per file to send, in order to avoid confusion. The bug report must mention which type of translation is sent (debconf, programs, etc.).