The more the mind is trained on learning languages, the easier it is to learn more and more, from any language.
Your mind can be trained to learn more than one language at a time, and your ability to learn any one language will be accelerated the more you are used to picking up more than one language.
The journey in which you take to learn one language, can be applied to learn other languages as well. Taken in parallel, your mind is forced to distinguish between each of the languages, and with minimal conscious effort, you could be able to learn at an amazing pace within the languages.
Bridges Between Languages
Within each language, there are words, phrases, expressions that are similar to that of another language. These various words, phrases, expressions, of which we are calling bridges, can be used and understood to help remember aspects of the different languages you are learning. Bridges are very useful and help you to continue to learn by association.
Build Bridges Between Common Languages
There are definite bridges that can be made among common languages, which tend to make learning languages in parallel easier. For example, if you choose to learn Latin, Italian and Spanish all at the same time, you will begin to see the similarity in structure and setup of the languages. This will make it easier, and almost natural for you to learn each of the languages at a faster pace. The same rules apply to languages of similar regions (i.e. Hindi, Bengali, Gujarati, Punjabi -OR- Korean, Chinese, Japanese -OR- Russian, Slovenian, Slovak).
Build Bridges Between Languages From Different Regions
For those that want to try and learn a large number of languages, it may be best to pick languages from distinct regions and then it can provide a broader perspective of not only the distinct languages, but the similar languages contained within. Amazingly at some point, even in the languages from distinct regions, you will begin to find similarities that make it easier to associate them together.
Capture Your Thoughts In Your Native Language, Replay Them Out Loud In the Language You Are Learning
By capturing your thoughts in your native language and then saying them out loud in the language(s) that you are learning, you are in effect overriding the natural response of your mind to help train it to respond with the other languages. This thought capturing technique can be a very effective method to help to condition your mind for learning languages as well. Carry a dictionary with you in the language you are learning to help you quickly look up all of the words and phrases you do not know, just to help you say at that time.
Multi-language Learning Techniques
The same techniques for learning one language apply when learning multiple languages. However, there has to be time invested for the number of languages that you are trying to learn. Review and practice the languages daily, and continue to train you mind to think in each of the languages.
Spend an entire period of time dedicated to thinking in one language at a time. For example, say you are learning Farsi, Chinese and German all at once. Throughout your day, you could wake up trying to think in Farsi, then later on switch to thinking in Chinese, and so on with German. Tomorrow, you could change which language is the first to be used. It is important to give due time to each of the languages, so that you can progress, and at the same time, your mind will continue subconsciously to associate the other languages with your actions as well.
Poliglota - Carlos Freire
Spanish : Ziad Fazah
An interview with Tony Hernandez: the joy of being multilingual
Hyperpolyglot (16 languages with captions in English)
Speaking Albanian after 3 lessons
Spanish : Un Esclavo
Language Learning FAQs: Multiple Languages at Once
Hyperpolyglot Emanuele Marini speaking in 16 languages!
Multilingualism is a life style for all
A Polyglot's Daily Linguistic Workout
Michal Grzeskowiak interview with Richard Simcott in English, German, Spanish and Polish
Polyglot tour of flat in 8 languages and 6 dialects