The main factor or play here relies on the definite article (AL) and where do you put it.
Your sentence, This cold bathroom does not bear an indefinite article (a), so even in English, a listener would understand that you are pointing to some known cold bathroom. This is because the pointing particle or article This takes the job of The when it's absent. So, just to make the idea clearer a bit, imagine we remove This and put The and your sentence will become The cold bathroom. In fact, it's not a sentence. You are simply naming some bathroom as the cold bathroom. You did NOT state that the bathroom IS cold.
That was the English analysis. As for Arabic, as I said before, things depends somewhat on the position of (AL) if it exists. Maybe some examples will elaborate:
- هذا حمام بارد: This is a cold bathroom.
- هذا الحمام بارد: This bathroom is cold.
- هذا الحمام البارد: This cold bathroom.
Notice each translation and the corresponding Arabic part for it, and notice how does the definite article (AL) stands in Arabic. One thing to make it clear (if you don't know already) is that the adjective in Arabic comes after the noun, and it follows the noun in its cases:
- If the adjective is attributive: As in English cold bathroom, these adjectives in Arabic follow the status of the noun in number, gender, AND definition.
- If the adjective is predicative: As in English the bathroom IS cold, these adjectives in Arabic follow the noun in number, and gender ONLY. Not the definition, as the predicate of the sentence in Arabic is (mostly, not generally) comes undefined with (AL).
Hope it this clears it up.