I am generally imagining a couple of missed words, like 'I like some food' instead of 'I'd like some food'.

 

Depends on how much time you want to spend on it. You could do different things depending on what languages are involved, but beyond surface level, most people won't recognise or appreciate the details. You could play around with tenses, like instead of 'I am going to go to the market on Sunday', you could have 'I go to the market Sunday'. Their vocabulary would be more limited too, so no highly specific terms for things. Sentence structure changes too depending on the language; for example 'Où habites-tu?' is 'Where do you live?' in French, but translated literally is 'Where live you?'. Pronunciation of certain letter combinations change language by language too, so you could work that in to their dialogue. 'Education' is spelt the same in French and English, but the 'ti' in English is a 'sh' sound, while in French it's a 'ss' sound. Likewise, the 'h' isn't pronounced in French, 'ence we 'ave Fleur 'orishly 'umming 'arry's name. Having these differences in the character's speech is a way to demonstrate their accent as well as their lack of grasp of a language, so long as you don't lose control of your life and end up with a monstrosity of a sentence with more commas than a Chiss surname.

I can't speak for the idiosyncrasies of other languages, but that's about how I'd do it. Basic word structure, and broader terms for things instead of more specific ones.

 

In speech question inversions are generally not used as much. You see them more in text. Usually you would just say "Tu habites où ?", which directly translates to "You live where?", or "Où est-ce que tu habites?, which translates kind of to "Where do you live?", with the "est-ce que" serving as an equivalent to "do" in English.

@Hot Salsa Broken English is extremely difficult to emulate because they're entirely dependent on the nuances of the individual who has the broken English. Every English learner, even from the same language, will make different mistakes, so there isn't much of a formula in doing it, you just need to draw whatever seems vaguely like it could be a mistake in English from another language as see if it doesn't sound too weird.

https://www.fanfiction.net/s/13050311/1/Betrayed

I wrote this trying to emulate broken English. Maybe you can draw something from it.