You can say "fellow citizens", I think, but only in the plural does it name the collective you want; the only snag is that the expression is practically confined to being used after a "Saxon genitive" , possessive adjective, or equivalent "of phrase): "The mayor's fellow citizens did not approve of the measure"; "His fellow citizens criticized his policy", "The fellow citizens of the mayor..." etc. The reason is that "fellow-X" is a relational term: it must be somebody's fellow-X), where X stands for "citizen", "student", "teacher", whatever, and "somebody's" corresponds to the possessive, genitive or "of phrase".

I don't know how to say it in English either, but there is a word in Spanish with the same meaning: "paisano"

I don't know Chinese, but in English we don't have a word for people of the same city. For people of the same nationality, you can use two words: countryman/countrymen (singular/plural), or compatriot/s. I hope this helps!

I too am not aware of a specific English term similar to lao xiang. The term "citizen", when used on its own, usually refers to people from the same country. However, when the word citizen is accompanied by a 'qualifying' term such as "my fellow ...", it will be clear who the term citizens applies to. There is one term that may be used in English ... "fellow townsmen" (men includes males and females), however this term is not used very often.