Yes, you can as long as these are either primary sources used for analysis or solid peer-reviewed high-quality studies. Just check the stylesheet and also the referencing system you use for how you deal with titles in another language.
Yes, you can. There are dozens of papers published in different languages such as Spanish, Portuguese, Russian, Romanian and Persian, but the research should include a summary in English usually.
Many of the RG members add their works in Russian, Arab, Hebrew, Spain, Italian and other languages. But it would be better if you add your texts also in English translation. My best regards to you!