Yiddish yidish ייִדיש (~ idish אידיש) ‘Jewish; Yiddish’, neuter ‘the Yiddish language’ < MHG jüdisch ‘Jewish’, jüdische (implied: zunge) feminine ‘the Jewish language’* (> German jüdisch ‘Jewish’)
* In the only quotation (the first quarter of the fourteenth century) given by M. Lexer for this meaning, the Hebrew language is meant; so also in an earlier text of 1293‒1313.
English Yiddish [ˈjɪdɪʃ] – attested since 1885‒1890, since 1875, or since 1871; but the variant Yedish is recorded in 1866
German jiddisch ‘Yiddish’, Jiddisch neuter ‘the Yiddish language’ – attested since 1880‒1889 (or 1915/1916?, but at any rate 1909); yet jiddisch-deitsch is attested in a purely German text at least since 1855
French yiddish ~ yiddisch (and several other variants) ‘Yiddish’, masculine ‘the Yiddish language’ – attested since 1907, but the form yudisch (< German jüdisch) since 1864 (see TLFi)
Polish jidysz (earlier also idysz and jidisz ~ idisz) masculine ‘the Yiddish language’, usually indeclinable – first attested probably in the 1920s, cf e.g. “Rocznik Orjentalistyczny”, vol. VI, 1928 (published 1929), p 273 (a notice on the establishment of the Yidisher Visnshaftlekher Institut in 1925, containing the variant idysz)
Russian идиш (earlier also йидиш) masculine ‘the Yiddish language’ – attested before 1930 (in the fourth volume of the “Литературная энциклопедия”, published in 1930, А. Зарецкий writes: “в последнее время распространяется название идиш”)
For various words for ‘Yiddish’ in Yiddish, Hebrew and some other languages, see M. Weinreich, History of the Yiddish language, chapter: 5. The name Yiddish, vol. I, p 315‒327 & A302‒A312.