You could translate it as "a pair of pants", and that's the appropriate way to put it in English, but really it says "one pants".
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(It's not the case, however, that all measure words require nouns. 天 ("day") and 年 ("year") are measure words that are almost always used on their own. There might be an implicit notion of "one day of time" or similar.)
You could translate it as "a pair of pants", and that's the appropriate way to put it in English, but really it says "one pants".