Strategies for reviewing a paper that has non-English references

I am reviewing a paper that quite heavily builds upon work that has only been published in Russian and Romanian, which are languages I (unfortunately) do no speak. Therefore it is quite difficult for me to assess how this new work builds upon this previous work.

This work was submitted for an English-speaking venue in which normally all papers only reference papers in English. At first glance, the venue only request the actual paper to be in English, but makes no mention about related work.

How to proceed?