Yes, knowing multiple languages can result in situations where you confuse between them, or blur the edges between them (eg using techniques suitable for one language when programming in another -- sort of similar to people speaking with accents). The approaches to addressing those issues are the same as for spoken languages: slow down, take more time, think more about how you wish to express something in the language you're using, etc etc.
As to what other languages you might wish to learn: what do you wish to achieve? For example, what types of applications do you wish to develop?
And people who learn assembly may be a little twisted, but that doesn't make them crazy
