I have the following idea. If you find the creation of interactive lessons easy and fun but you do not want to create your own book then you can consider participating in my small project. Make a very small book in your native language (can be just one lesson). Do not fill the fields for the translation etc. that require knowledge of a foreign language (you can type your comments and directions in your own language there) and e-mail me this small book. If I receive many small books with the English, French, German etc. lessons I will make a bigger template book (or books) by joining them. I will submit them as freeware templates for these who want to adopt them for teaching particular language.
For example, if I have the template book in English I can add the Polish part to it and make it a course of English for Polish speakers. The same can be done for many other languages.
The requirements for your small template are:
• it should be small (no more than 500kB compressed),
• you have to give up your copyrights to your small template (it would be difficult to deal with so many copyrights terms when the book includes work of so many people) and release it to the public domain.
I will list all the contributors to the template and release the template as PD but I am not going to bound the template users (authors of books based on these templates) with any copyrights problems (so they will be free to make modifications and sell or give away their books based on these templates).
Please do not use the "best" sound quality. The "better" quality is sufficient. The "good" quality is also sufficient in some cases and it saves a lot of disk space.
I hope that this idea can be interesting because a book created by so many authors will not be boring (but somewhat chaotic I suppose).
You can of course prepare your own complete books and distribute them commercially or as a shareware (freeware) with all your copyrights. You can easily protect your book with a password so the final user cannot modify it. You can also set the "demo" password so users will use your book in a demo mode until they pay you the fee.