Learning multiple programming languages is good practice and is necessary nowadays; as many times you can't always use your language of choice for everything.

The benefits of seeing how other languages do things will help you as a programmer; even if occassionally when you are jumping around you make syntactical mistakes (e.g., is checking for inequality !=, ~= or <>). You should be careful though to learn more than just the syntax of a language, but best practices within a language as well as just general good software engineering skills. Stuff if you learned C and then learned C++ you should make sure when you are writing C++ code that it is in the style of C++ code (rather than just C with a few new keywords. That is you have multiple classes/objects, prefer references/smart pointers over raw pointers, etc.