What question you didn't ask? WHY ImTranslator HAS DUPLICATE LANGUAGE DETECTION OPTION?
You may have noticed the "DETECT LANGUAGE" item in the source language list, which is set as default after the initial ImTranslator's installation.
There is also "DETECT SOURCE LANGUAGE AUTOMATICALLY" item in Options for each translation application.
LET US EXPLAIN WHY
The language detection feature is a very sophisticated mechanism. When you use "Detect language" in the the source language, it does a good language detection job for large portions of texts.
But there may be cases when the language detection tool doesn't recognize the language correctly especially for languages of the same language group, loan-words or short text. If you work with the Dictionary or with a pair of languages with the English language, the "automatic language detection" does a more advanced job.
a) Let's say you translate from French to English. But your translation direction is set to English - French. The automatic language detector identifies that the target language of the translation direction is identical to the language of the original text, and does an INSTANT LANGUAGE SWITCH to French - English, when you press the Translate button.
Don't you agree that this is very convenient and save your time and clicks?
b) Here is another case. You translate from French the word "succession". But the automatic language detection insists that this word is English.
You definitely know that this is the French word, and you disable the automatic language detection on the fly by choosing the French language from the source list and locking the language (marking the lock-in checkbox).
You do it on the fly, without accessing Options. This also save you time and clicks and make your translation work very user-friendly.
So, as you can see the language detection is an advanced language option, which may give you some great benefits in your translation work.
Language Detection in Chrome
Language Detection in Firefox
Language Detection in Opera