Translation

Will you please tell if you understand the following text? Are there grammar mistakes or ambiguity? It is a translation from Bulgarian into English. Thank you!
" In the 9th century the brothers Cyril and Methodius upset the trilingual dogma and created the alphabet of the Slav peoples. For more than a thousand years the Cyrillic alphabet has been one of the few officially recognised languages along with Hebrew, Greek and Latin for spreading Christianity among the peoples of Europe. Bulgarians honour the 24th of May as "Sts. Cyril & Methodius Day". All over the country schools are decorated with flowers and portraits of the brothers St. Cyril and St. Methodius in gratitude for the treasure of letters so suitable for the pronunciation of the Bulgarian language.
The occasion is closely related to the lives and deeds of the two missionary brothers, Sts. Cyril and Methodius, who developed the first Bulgarian alphabet (Glagolic) to accurately reflect the sounds of the Bulgarian language. Millions of people read and write using this alphabet; not only in Bulgaria, but also in Russia, Serbia, and even Mongolia. "

Very nice translation. The acid test of a good translation is this: Can you tell that it was originally written in a foreign language? I can't tell, so it passes that test. :)

Only one minor point: In the text you say that the Cyrillic alphabet has been one of the few officially recognised languages for spreading Christianity. It isn't a language, it's a writing system. I suspect the original is badly written, because the Cyrillic, Latin, Hebrew and Greek alphabets are the only scripts in common use in Europe (you might include Arabic if you consider Palestine as part of Europe), so the sentence doesn't make much sense. However, I would consider changing "languages" to "writing systems"; I would also (if you are charging money for the translation) get in touch with the author of the original and ask for clarification.

Thank you very much !