In a recent post on his blog, Tim Ferriss explains how he deconstructs languages in order to get an idea of their structure, grammar, sound system and writing system. This gives him an idea how long it will take and how difficult it will be to learn each language and helps him to decide whether or not to do so.

His method is the find native speakers, ask them to translate a number of sentences into their language, writing them in their native writing system, if one exists, and in transliteration. The translations of the sentences give him an overview of verb conjugates, word order, whether or not noun cases and/or auxiliary verbs are used. If possible, he also asks the native speakers to give examples of words for each consonant and vowel.

Some of the sentences he uses include:

The apple is red.
It is John’s apple.
I give John the apple.
We give him the apple.
He gives it to John.
She gives it to him.
I must give it to him.
I want to give it to her.

He suggests that before you take the plunge into learning a language, it’s worth your while finding out just what you’re letting yourself in for. He compares it to a return on investment – with some languages you will get a much better return, i.e. you will learn them more rapidly, than with others.

I also found an interview with Tim Ferris in which he discusses some of his techniques for learning languages.