Saying Thank G-d:

It is forbidden to recite an unnecessary blessing whether in Lashon Hakodesh or a foreign language.[1] Based on the above ruling, one may not say “Brich Rachamana” in Aramaic, or “Danken Got” in Yiddish, [or “Thank God” in English, or “Gracias a Dios” in Spanish, or “Alhamd Lilah” in Arabic, “Slava Bogu” in Russian[2]], unless it is being said out to express a true joy of the heart. Thus one should warn people who are accustomed to say these terms casually even when there is no joy of the heart to not do so.[3]  [Nonetheless, many are lenient in this matter.[4] To note, that this negation is only regarding saying God’s name in a blessing, such as saying “thank God” or “blessed be God,” however, to simply say the word God in a sentence is permitted when done for a purpose, as explained in A that only blessings are prohibited from being recited unnecessarily even when done for a purpose.]

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^[1]  Seder Birchas Hanehnin 13:4; Luach 12:10; P”M 219 M”Z 3; Shut Rav Akiva Eiger 25; Haemek Sheila Yisro Sheilasa 53:2; Kaf Hachaim 215:25; Encyclopedia Talmudit ibid p. 282 footnote 22; Piskeiy Teshuvos 215:12 and 18

Other opinions: Some Poskim rule that the prohibition against saying a blessing in vain only applies when it is said in Hebrew and not when it is recited in foreign language. [Pnei Yehoshua Brachos 12a; See Pischeiy Teshuvah Y.D. 328:1; Encyclopedia Talmudit ibid p. 282 footnote 23]

See regarding that God’s name foreign languages contains holiness: Seder Birchas Hanehnin 13:4; Luach 12:10; Admur 85:3; Bach 84; Olas Tamid 85:6; Ateres Zikeinim 84:3; Shach 179:11 [Kuntrus Achron 85:1]; Bach, brought in Shach Y.D. 179:11; P”M 219 M”Z 3; Kitzur SH”A 5:10; 6:3; Chesed Lealafim 85:2; Urim Vetumim Urim 27:2; Nesivos Hamishpat Choshen Mishpat 27:2; Smeh; Aruch Hashulchan Choshen Mishpat 27:3 in name of many Gedolei Yisrael; Ketzos Hashulchan 5:41; Encyclopedia Talmudit ibid p. 429 footnotes 161-164; For dissenting opinions, see: Rama 179:8; Shach Y.D. 179:11;Chavos Yair 106 regarding if written in non Ashuris letters; Shiltei Giborim Perek Kol Kisvei; Shabbos 115a; Admur 334:12; M”A 334:17; Rambam Shaar Hatziyon 334:27; See Pischeiy Teshuvah Y.D. 276:11; Sdei Chemed Kuntrus; Igros Moshe 2:55; Minchas Yitzchak 1:17

[2] See Admur 85:3

[3] Seder Birchas Hanehnin 13:4; Luach 12:10; See Piskeiy Teshuvos 215:18 footnote 105 who on the one hand writes that one may say thank God in response to how he is doing being that he is saying God’s name in a way of praise however he then writes that it may not be said out of habit

[4] See Halichos Shlomo 22:9; Piskeiy Teshuvos 215:18 footnote 107