I have a site with multilingual website with many pages (40M). The site has UGC, and each translation is actually for the titles. Each sub-domain points to the same content with different titles per language. As far as I understand, each sub-domain should be indexed by search engines, meaning they will actually need to crawl 40M x supported-languages. So I thought it might be best to direct each subdomain crawler, to pages that are fully in that language (titles + UGC).
Is there a way to do this? Should search engines understand this on their own?