I have come to categorize languages as continuum between "Reversible" at one end, and "Irreversible" at the other.
Now what do I mean that? Some definitions are in order.
Reversible languages: Those languages that can easily be pronounced as you read. It is sort of "you get what you see". The reversibility comes from the fact that you will be able to write what you hear. That means there are not too many silent letters in a word. That would also mean that vowels are pronounced in one and only one way.
Many of the Indian languages, such as Hindi, Bengali, etc., are completely reversible. German, inspite of umlauts, is primarily a reversible language.
Irreversible languages: Those languages that can be easily pronounced as you read but try writing what you hear and you will hit a wall. These languages have silent letters by the dozen. These also have group of letters that are pronounced in a particular way. I can think of French as an irreversible language. Once you get the hang of the pronunciation scheme it is more or less easy to read out. But since there are too many silent letters, many words sound almost identical, separated only by nuances of nasal tone.
Rest of the languages fall within this spectrum. English is a classic case. The language not only has silent letters it also has non-deterministic pronunciation key, i.e., same set of letters / vowels can have pronunciation is multiple ways, example, but - put - cut. Sometimes different words can have the same pronunciation but can have different spellings. Example, but - butt (sorry, nothing else comes to mind readily), route - root (we will not cosider the American pronunciation of route),. Sometimes, same spelling can give you different pronunciation. Example, "aged" has two pronunciation - aged and ag'ed - both having different meanings.
So how does this classification help us is learning?
Reversible languages can be taught in any way. One could start by hearing the language and then reading it. These can easily be taught using an iPod, for instance.
Irreversible langauges need simultaneous hearing and reading. Like French. Though it is better to start with reading; iPods must be accompanied with reading material.
The languages that fall in-between (confused languages?) are the most difficult to teach. I am glad I am not an English teacher.