The TMGMT method can be used to translate i18n strings. It uses all the mechanisms defined by i18n.

Once you turn on all the necessary modules (i18n, string translation, menu translation, block languages, taxonomy translation etc.), the chosen strings will show up on the Admin > Translation > Sources page. In our case Blocks, Menu and Taxonomy strings.

It may be neccessary to refresh the strings (Administration > Configuration > Regional and language > Translate interface > Strings) before they become visible.

As an alternative, you can choose to request a translation from the translate tab of any given element.

The TMGMT process is the same as for content and entity translation.

A word of caution

Be careful to understand the intricacies of interface translation in Drupal before jumping into using TMGMT on strings! TMGMT manages ONLY the translation process, not the usage of the strings.

Should you choose to make the entity bundle 'taxonomy' translatable and allow string translation for taxonomy terms on the same site, there will be two 'taxonomy' pages on the Souces page. This can be very confusing and the outcome is quite unpredictable.