This is a thread for translating cards posted on this sight. I prospect it is enough possible that only I post on this thread but it's OK. If you post here, please add a note why you translated so. It's fun to know other language's trivia. Comments on a wrong translation are welcomed.
I cannot fluently write English. If you found more appropriate or cooler words for my card name, flavor text or post, I will be glad to hear your advice.
チープ鶏ック/Cheep Trick This is easy. チープトリック( Chiipu Torikku ) is the transcription of cheap trick. Most of us understand the word without translating into Japanese. 鶏 ( tori ) is chicken. Embedding 鶏 into the place where the transcription has same sound then チープ鶏ック.
小人神墟/Idol Hands We have a similar proverb 小人閑居して不善を為す which literally means "poor man does evil thing when he get bored". The first part 小人閑居( Shou Jin Kan Kyo ) means poor man get bored. The art is an archaeological sites so change 居 into 墟, which has same sound and means archaeological sites. 神 is god and can be read Kan so change 閑 into it corresponding to idle to idol. In here, god is not literally meaning but alluding religion.
冷やカスマイア/Myr Trifle 冷やかす( hiyakasu ) is tease, mock, make fun of. カス( kasu ) is garbage, dust. マイア is myr. 冷やかす and カス into 冷やカス to mean trifle's two meanings which are small thing and making fun. But I am not confident that I am understanding this joke because this card is small thing but unblockable and teasing don't share so close image.
マーク・オヴ・ローズ・アンド・ウォーター/Mark of Rose and Water Totally a transcription. But Most Japanese can understand all of the words so they can image what the name means. Many Forgotten Realm spells translated as transcriptions for magic items and spells in D&D were originally transcripted. So this is not so strange translation.
頭痛厄/Painkiller 頭痛(zutsuu) is a headache and 厄(yaku) is curse, disaster or unluckiness. 頭痛薬( zutsuu-yaku ) is a medicine for headache. I am not fully satisfied with this translation for medicine for headache is not equal to painkiller but I preferred it rather than another candidate. Another candidate is 痛み止め( Itami-Todome ). Generally, 痛み止め is read as Itami-Dome and means a painkiller. 痛み( Itami ) is pain and 止め(Dome) is to stop. 止め has some meanings and some pronunciations. When you read it todome, it is to deliver the coup de grace. So, Itami-Todome means killer with painful way of killing. The reason I don't choose this is that it is not punny. It is not intuitive for us and takes a bit second to comprehend it is joke. In a view of keeping the original meaning, 痛み止め is better. But Painkiller is very easy to understand that it is a joke and no sound changed from original word. I regarded the latter element highly.
かわずかな記憶/Brain Frog かわず( kawazu ) is an old name for a frog. Most of Japanese can understand it means a frog though a bit archaic. わずかな記憶( wazukana kioku ) is a faint memory. Literally translation for brain fog is not so normal expression in Japanese. It is mainly used like "I feel my brain is shrouded by mist" and not used as a noun. か（ ka ）is very old adverb that means "very". It is alive in recent Japanese in limited combinations with certain adjectives. Ka and wazukana combination is not used usually but it is not grammatically wrong. A little Japanese who are well informed about Japanese will notice it is a pun of frog and "very faint memory".
忘れ字の泉/Font of Nostalgia 忘れ字 ( wasureji ) is a portmanteau of 忘れじ( wasureji ), which is very old phrase that means "I will never forget", and 字( ji ), which means a character. の(no) is of and 泉(izumi) is a fountain. Font cycle in Theros is translated as "～の泉" ( fountain of ... ) so I want to keep this format. But 泉 doesn't have a meaning of character so I moved the meaning of character from Font to the part of Nostalgia.
臥薪瘴弾/Blight the Bullet Portmanteau of three words. 臥薪(ga-shin) is the first part of 臥薪嘗胆(ga-shin-shou-tan). Each character means sleep-firewood-lick-liver. It is after a Chinese story of two lords. A lord had slept until his avenge was done. Another lord used to lick bitter livers until his avenge was done. Both lords took suffering willingly in order not to forget their will to avenge. 瘴 ( shou ) is poisonous miasma. Kokusho's sho is also 瘴. 弾 ( dan ) is a bullet. There's more similar phrase for bite the bullet than 臥薪嘗胆 but it is hard to portmanteau with any word that is a kind of a bullet. The art shows a gun and the flavor text says about the bullet, so it is inevitable to use a word among gun, bullet, shoot etc.
回転泥棒/Motion Thief Notion Thief is 概念泥棒( gai-nen-doro-bou ) in Japanese. 概念 is notion, concept and 泥棒 is a thief. The crux of this pun is it only differs in M and N from the original so I chose the word according to it. 回転( kai-ten ) is to rotate and it implies untap.