Problem/Motivation
It looks like there is a missing condition on i18n_string.objectid in the d7_term_localized_translation source plugin.
As a result the first tid gets migrated correctly but all of the following tid (taxonomy terms) get the values from the first one.
Shouldn't we add: ->condition('i18n.objectid', $object_id);
in core/modules/taxonomy/src/Plugin/migrate/source/d7/TermLocalizedTranslation.php:73
Proposed resolution
The taxonomy term translation source plugin should use I18nQueryTrait properly. It is included but not actually used, as if it was intended to be used but was forgotten.
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