From Wiktionary, the free dictionary
The adage originates from the common craft of blacksmithing . It appears in Chaucer's The Tale of Melibee Harvard )
It gained additional meaning when used as a motto by Joseph Paisley - a blacksmith at Gretna Green who married eloping couples at his anvil. (History in the Margins )
Striking red-hot iron strike while the iron is hot third-person singular simple present strikes while the iron is hot present participle striking while the iron is hot simple past and past participle struck while the iron is hot
( metallurgy , blacksmithing , literally ) strike a hot piece of metal , especially iron , with a mallet or other tool before it cools , while it is still hot enough to be shaped .( idiomatic ) act on an opportunity promptly while favorable conditions exist; to avoid waiting .
We should strike while the iron is hot and order some immediately, before they change the offer.
c. 1620s Elizabeth Cary [misattributed to Henry Cary ], The History Of the most unfortunate Prince King Edward II. [ … ] , London: A.G. and F. P., published 1680 , page 41 :The Gap thus stopp'd, with her Army she marcheth to the Cage that kept those Birds, whose Wings she would be clipping. She knew if she struck not while the Iron was hot , the heat of a popular Faction would quickly sink and lessen.
When expressed in the imperative mood, this term is a well-known saying or proverb:
Strike while the iron is hot !
act on an opportunity promptly
Albanian: hekuri rrihet sa është i nxehtë
Azerbaijani: dəmiri qızğınkən döyərlər dəmir isti-isti döyülər
Chinese:
Cantonese: 趁熱打鐵 / 趁热打铁 ( can3 jit6 daa2 tit3 ) , 打鐵趁熱 / 打铁趁热 ( daa2 tit3 can3 jit6 )
Hokkien: 魚趁生，人趁茈 / 鱼趁生，人趁茈 ( hî-thàn-chhiⁿ, lâng-thàn-chíⁿ )
Mandarin: 趁熱打鐵 / 趁热打铁 (zh) ( chènrè-dǎtiě ) , 打鐵趁熱 / 打铁趁热 (zh) ( dǎtiě-chènrè )
Czech: kout železo, dokud je žhavé kuj železo, dokud je žhavé (cs)
Danish: smede mens jernet er varmt
Dutch: het ijzer smeden als het heet is
Finnish: takoa kun rauta on kuumaa (fi)
French: il faut battre le fer pendant qu’il est chaud (fr)
Georgian: დაჰკარ, სანამ რკინა ცხელია ( dahḳar, sanam rḳina cxelia )
German: man muss das Eisen schmieden, solange es heiß ist (de)
Greek: στη βράση κολλάει το σίδερο ( sti vrási kolláei to sídero )
Hebrew: הכה בברזל בעודו חם
Hindi: लोहा गरम हैं. मार दो हथौड़ा. ( lohā garam ha͠i. mār do hathauṛā. )
Hungarian: addig üsd a vasat, amíg meleg (hu)
Irish: buail an t-iarann te
Italian: battere il ferro finché è caldo
Japanese: 善は急げ (ja) ( ぜんはいそげ, zen wa isoge ) , 膳は急げ ( ぜんはいそげ, zen wa isoge ) , 鉄は熱いうちに打て ( てつはあついうちにうて, tetsu wa atsui uchi ni ute )
Korean: 쇠뿔도 단김에 빼랬다 (ko) ( soeppuldo dan'gime ppaeraetda )
Lingala: otútá ebendé ntángo ezalí na mɔ̌tɔ
Lithuanian: kalti geležį, kol ji karšta
Macedonian: железото се кове додека е жешко ( železoto se kove dodeka e žeško )
Maltese: il-ftira sħuna tajba
Norwegian: smi mens jernet er varmt (no)
Polish: kuć żelazo, póki gorące (pl) impf
Portuguese: malhar enquanto o ferro está quente
Romanian: bate fierul cât e cald
Russian: куй желе́зо, пока́ горячо́ (ru) ( kuj želézo, poká gorjačó )
Serbo-Croatian: željezo se kuje dok je vruće
Spanish: al hierro caliente batir de repente batir el hierro cuando está al rojo
Swedish: smida medan järnet är varmt (sv)
Thai: ตีเหล็กเมื่อแดง กินแกงเมื่อร้อน ( dtii-lèk-mʉ̂ʉa-dɛɛng-gin-gɛɛng-mʉ̂ʉa-rɔ́ɔn )
Turkish: demir tavında dövülür (tr)
Walloon: bate li fier tant k' il est tchôd ploumer l’ ålouwete cwand on l’ tént (wa)
Gregory Y. Titelman, Random House Dictionary of Popular Proverbs and Sayings , 1996, →ISBN , p. 309. 
