Yeah, I know this, it's horrible. My problem is with speaking French, Spanish and Italian. Only one of the languages is fine, but once there are two or more, I start mixing words together really badly.<p>I think it's because those languages are so close to each other - like C++, C# and Java - which was probably the reason I could become reasonably fluent in each of them in the first place. I actually learned Italian by "prototypal inheritance", gradually substituting Spanish words and grammar as I learned their Italian equivalents while living there.