Words are words, as far as I am concerned, code or not. So have a look over the module and see where you think the words can be improved. All the help files, such as this one, can be found in the folder 'help'. You don't need anything but a text editor to change them. If you don't know HTML you can ignore the tags, and change the words. If you get a bit better then a HTML text editor, such as Bluefish will help put tags in. I suggest you avoid word processors with HTML abilities (Word/OpenOffice) as they spew out formatting garbage. I also recommend you avoid complex webpage creators (e.g. Dreamweaver) as they are slow, and make unhelpful assumptions.
By the by, this module now uses Advanced Help for it's main help system, and I can't think of a better place to start to learn about HTML or take the first steps to coding something real.
Also, pictures and diagrams are great, but time consuming. So if you fancy a go with Photoshop or the GIMP, please do! We'll stick them in for you if you don't know how.
Any module will recieve pages of usability reports, but you might also consider properly testing the module. We'd be very glad to help out and point where to go, and immensely grateful for the results.
So you know a little PHP? Great.
In contradiction to most coding practice, I litter my code with comments. It's untidy, and harder to read, but within a fast evolving module to which I can't give sustained development, the comments help me pick up where I am. So all you have to do is cruise round the module (taxonomy_treemenu.module and taxonomy_treemenu.admin.inc are the best places) looking for the //TODO: and //TO CONSIDER: marks.
Some areas are a bit fiendish. For example, you need a basic understanding of object orientated code to handle anything to do with Views or Taxonmy Treemenu's own options query builder. But some are ridiculously simple. For example, the churning development means that there is always a certain amount of renaming that needs to be done, and functions to be tidied up.
Some information which may help; I was a beginner to PHP coding when I started this project.
Uh hu? What's your expertese? You're probably better than me, anyhow.
The interface of this module is misleading. It's been refined to become very simple, a page of Drupal-looking form. The form is not as simple as it looks, and the code is large. This is not UberCart, or Views, but it heads in that direction. The two issues are these. First, the module ranges over a vast swathe of Drupal. It interfaces with the Taxonomy, the menu system and the form API, primarily. Along the way that means taking in caching, JQuery, other API's (e.g. Views and PathAuto), and many more interfaces. The second issue is that we have to glue all this together.
One approach is the jolly fine open source approach of fixing what you don't like. In Taxonomy Treemenu this is easy to set on, as I've never tried to make 'cute' code, prefering to sketch out an area and provide basic functionality. Sometimes this is a success, such as the menu rendering in Version 1. Sometimes a failure, such as the Views integration in Version 4.2. But the failings and abilities of the code are usually evident when using the module.
Another approach is if you have base knowledge about some area. You can go for that, or dive in, knowing as you do, that you have the skills to take it on. If you feel adventurous, I usually have a longish TODO list of fixes, changes, updates, and new/depreciated features. So post. I'll give you the low-down on what is going on, and we can take it from there.
As for working on the code, it is always exceptionally untidy, littered with comments and dpm()s. But then, that means it is informative if you want to know where to start.