In translation, the source language is the language being translated from; it is the antonym of the target language, which is the language being translated to. Part of the difficulty in translation arises due to the lexical gap between the source language and the target language. The necessity of translation arises from that gap, especially between two languages belonging to different language families.
In most professional settings, the source language is also the translator's second language. The process typically begins with a full and in-depth analysis of the original text in the source language, ensuring full comprehension and understanding before the actual act of translating is approached.
To confirm the authenticity of the translation, back-translation is sometimes used. That means a text is translated from the source language to the target language; a second translator then translates the translation back into the source language. The two source language texts - the original and the back-translation - are then compared for discrepancies.