Russian Jews speak Russian as their first language. Yiddish is a rare second language in Russia. Hardly any Russian Jews can speak it (Most Yiddish speakers in the world live in Belarus, Israel, and Argentina).There are no longer any native speakers of Yiddish in Russia.
Yiddish
It's mostly the Orthodox Jews.
English, Hebrew, and Yiddish.
They have no reason to speak Yiddish. It is or was the main language of most Ashkenazi Jews and is largely based on archaic German.
"Redstu Yiddish" is Yiddish for "Do you speak Yiddish?"
To say something in Yiddish, you would use the Yiddish language. Yiddish is a Germanic-based language spoken by Ashkenazi Jews and has its own unique vocabulary, grammar, and pronunciation. You can find resources online or take classes to learn how to speak in Yiddish.
"Shalom" in Hebrew. (Jewish is not a language unless you are referring to Yiddish, which is another category on this site.)
Ashkenazi Jews live all over the world and speak the languages of their countries. The most common languages spoken by Ashkenazi Jews are:EnglishHebrewFrenchRussianSpanishYiddish**Yiddish was once the main daily language of Ashkenazi Jews, but today less than 1 million can speak it fluently, and most of these speakers are elderly. Fluent Yiddish speakers mainly live in Belarus, Israel, and Argentina.
Most Orthodox Jews used to speak Yiddish. It was primarily spoken in Europe, but it was also spoken in other countries. Today, it is spoken by some Jews. Many Rabbis and older Jews speak Yiddish. Yiddish is the "Patois" of languages of every eastern European country with any significant Jewish population during the past 600 years. Dormant for a while after the great Jewish migrations of the early 20th Century and the mass exterminations of the 1930s and 40s, it's experiencing a resurgence today.
For a very long time the native language of German Jews has been German. Since the collapse of the Soviet Union (1991) a significant number Jews from the former Soviet Union (perhaps as many as 150,000) have settled in Germany. The second generation generally speaks German, the first generation a range of languages, which often includes Russian and Yiddish.
Moses Mendellsohn did not have to teach German Jews how to speak German. They were already very capable of doing so themselves. Those German Jews who chose to speak in Yiddish did so by choice (as a symbol of their Jewish identity).