Importing a limited number of languages

Dear Multiterm experts,

I have an export file of the Multiterm base that contains multiple languages. But I want to import only 3 of them.
I thought I could edit the termbase definition (delete unnecessary languages) and then import with "Allow over-complete entries" selected. But it seems that it does not add entries, if there are not only terms in required languages but also in languages missing in the termbase definition. E.g. if I do not change the termbase definition it imports 25000 German entries including 3000 Russian terms. If I change the termbase definition and leave only German, English and Russian it imports 20000 German entries including only 12 Russian terms.
What is the right way to import a limited number of languages from the multilingual termbase export?