There have probably been 20 or 30 artificial languages created in the last 100 years or so. Esperanto and Ido are probably the two best known in America, however I have found that several of the other languages are quite logical and easy to read.
Interlingua, Occidental, Lingua Franca Nova and Novial are probably the best known. Personally I am partial to Latino sine Flexione, perhaps because I studied Latin in school. I believe that anyone who is reasonably intelligent and can read any of the modern Romance languages can probably quickly become literate in any of these constructed languages. I think that all of these languages were based on Romance languages I also believe that there is Slavic constructed language called Slovianski.
Is there a Germanic constructed language? Although I am a native English speaker and understand a little German, I believe that a Germanic constructed language would be difficult for me to pick up very quickly.
Maybe it is because of all of the Latinate words that are in English.