I'm a Slovenian-American, so I'll attempt to answer some of your questions.
>>Is everything written in your countries language or are they some things written in English to make it simpler.
Many Slovene companies have English names. There are two reasons for this: English is very popular among Slovenia's young people, and Slovene pronounciation tends to give foreigners a really hard time. Some people are even sponsoring a bill that would require companies to use Slovene-language names. However, the bill also has many opponents and is unlikely to ever become a law. It is a generational thing: Many young Slovenians like the English names, while many older citizens fear that the Slovene language may eventually die out.
>>"Are all your magazines and books and instructions on how to use equipment all written in your language, percentage wise, I was wondering in the smaller countries whether the market would be big enough to make translations affordable."
In the big downtown bookstores, more than 50% of all books displayed are in English. Most people who frequent these stores have some knowledge of English. Many popular books, especially fiction, are translated into Slovene (even though there are fewer and fewer government subsidies for that), but most specialized books are not. Coffee-table books are almost never translated. Just the opposite, in fact: Many coffee-table books about Slovenia are also published in English for foreigners.
In short, most Slovenian publishers are more concerned about publishing original works than translating English-language books (except best-sellers). After all, most young urban residents understand English well enough to read books without a translation.
As recently asa few years ago, Slovenian-language instruction manuals were rare. However, a new law requires all such booklets to be in Slovene. Some companies, such as Micosoft, actually print their official booklets in Slovene. Often, however, the distributor that puts together a special Slovene-language supplement to go with the official instruction book.
Computer programs and operating systems, such as Windows, are available in Slovene.
Television pograms and movies are never dubbed; they are always subtitled. Cartoons are usually dubbed, however.
>>"Are books like Airways & Airliners available."
English language books on aviation are available in Slovenia. However, only one bookstore (as far as I know) has a large selection of them. English-language magazines (even specialized ones) are also widely available.
>>"How many people speak English, percentage wise to carry out a decent conversation."
Most young people, and those living in the cities, speak English well. Most older people, and those living in the country, do not. I'm not sure about the exact numbers.
And before anyone gives me a hard time: Both the words "Slovene" and "Slovenian" are perfectly acceptable. I use them interchangeably.