The Greek terms that are translated as “five thousand” and “four thousand” in these verses have to be translated descriptively in some languages, such as “ant heap” (Shona) or “large/uncountable number” (Chichewa, Yao).
See also numbers in Kombai.
Following are a number of back-translations of Matthew 14:21:
Many languages use a “body part tally system” where body parts function as numerals (see body part tally systems with a description). One such language is Angguruk Yali which uses a system that ends at the number 27. To circumvent this limitation, the Angguruk Yali translators adopted a strategy where a large number is first indicated with an approximation via the traditional system, followed by the exact number according to Arabic numerals. For example, where in 2 Samuel 6:1 it says “thirty thousand” in the English translation, the Angguruk Yali says teng-teng angge 30.000 or “so many rounds [following the body part tally system] 30,000,” likewise, in Acts 27:37 where the number “two hundred seventy-six” is used, the Angguruk Yali translation says teng-teng angge 276 or “so many rounds 276,” or in John 6:10 teng-teng angge 5.000 for “five thousand.”
This strategy is used in all the verses referenced here.
Source: Lourens de Vries in The Bible Translator 1998, p. 409ff.