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Moved to library forum as requested
The language column does not contain the English word for the language, but instead contains the
ISO 639.2 code for the language. This code is translated to the localized equivalent of the language name when it is displayed.
The easiest (and fastest) way to solve your problem is to use the ISO code in the color expression, in this case "eng". You could also do it using a more complicated template that uses the language_codes function, but I don't see any advantage to this method.