This is probably the question I get asked most often.

Actually, this is a very bad idea. Unless you are a seasoned polyglot, you will waste your energy, study time and will power over several languages and never reach an advanced level in any. It is much better to focus on one and only language until you become fluent, then move on to the next one.

Finish the language you are doing before moving on. This also applies to closely related languages such as Spanish/Portuguese or Italian/French. It’s much easier to build from a strong background in one language rather than trying to build concurrently the foundations of two languages.

Once you reach an advanced level in your target language, you can start a new language, and still work on perfecting the first one. But you cannot perfect a house without a roof. Once you are able to read newspapers, listen to radio and TV and speak with people on a variety of topics, you are ready to move on to another language. Of course, all your life, you will keep adding new vocabulary and improve your fluency in the first language, but this can be done simultaneously with learning a brand new language.

Keep your enthusiasm for a new language inside yourself and use the energy to move forward with the one you are studying now. Then move on to learn the new one. That way, after a few years of study you will become fluent in several languages, not just be able to chit-chat in half a dozen languages like a taxi driver in a tourist resort. ‘You want hotel? Me can show you discotheque? You buy souvenir?’.