Mojibake (Japanese: 文字化け; IPA: [mod͡ʑibake], ‘character transformation’) is the garbled or gibberish text that is the result of text being decoded using an unintended character encoding.[1] The result is a systematic replacement of symbols with completely unrelated ones, often from a different writing system.
Spoken languages using different letters.
It’s mostly an artifact of single-byte encodings where opening a file written in codepage X (say Codepage 866) with an editor using different codepage i.e. IBM437 - standard us english would result in garbage text.