And I found another big source for Russian sentences. United Nations documents published under PD, and there is already tagged corpus available https://cms.unov.org/UNCorpus/ I wrote a script that extract only proces-verbaux (transcripts) records from corpus and validate it using same method sentence-collector use, and got more than 300k unique sentences. Not all sentences are good, so they need to be validated by human additionally. Should I upload it to sentence-collector fully?
It also can be useful for other United Nations official languages (Arabic, English, Spanish, French, Chinese).