What is Source Language?

The source language is the language your content is authored in and translated from. In most software projects it is English, both because teams write in it and because translator availability and machine translation quality are strongest for English pairs, but nothing requires that; the source language is simply whichever version is the reference.

Everything in the pipeline keys off it. Coverage is measured against the source key set, translation memories store pairs from source to target, and when a source string changes, every target translation of it becomes outdated. That last mechanic is why source-side discipline matters: gratuitous rewording of source strings invalidates work in every language at once.

Source quality is also the ceiling on translation quality. Ambiguous, idiomatic, or inconsistent source copy produces divergent translations in every target language, and a fix in the source is cheaper than fixes in each of them. Writing source strings plainly, with context notes for translators, is the highest-leverage editing pass in the whole workflow.