"My lighter is new."
Translation:Mein Feuerzeug ist neu.
What about it? Only kidding. No you can't translate it like that, because you are mixing different words. "Lighter" in english has two meanings. One for a thing that produces a tiny flame and one meaning less heavy. The first one translates to the german "Feuerzeug - fire stuff" and the second one to "leichter". But you can't use "leichter" for "Feuerzeug", not even if you capitalize it.
If that's true, it's an error and needs to be reported. Maybe you come across it again. Modern German (newer than 200 yo) doesn't know a sound (or diphtong) "eü", you can just find this combination of letters in composita like "Lageübermittlung" where they are two independent sounds ("Lage-Übermittlung").
A very common sound shift is au -> äu, like in Haus (sg.) -> Häuser (pl.) or sauber (adj.) -> säubern (verb).
Also, the plurals of composita never change in the first word (Feuer-), but only in the second (-zeug -> -zeuge), as you would do it in English (e.g. power plant -> power plants, germ. Kraftwerk -> Kraftwerke, not powers plants and Kräftewerke).