Wow, you know the handwriting letters too! Svaka cast! Skidam ti kapu! I remember when i was a kid, i used to say i would never learn it cause it's too hard, hehe... Anyway, you are really really good at Serbian...
Misti is beautiful! I adore cats! But there are some mistakes there too... But those mistakes are usual for foreigners.
Volim da sednem na FejlicinU beležnicU. (verb SESTI; accusative)
or
Volim da SEDIM na Fejlicinoj beležnici. (verb SEDETI; locative)
Both "sesti" and "sedeti" mean to sit, but there is a difference... You noticed that Serbian language doesn't have continuous tenses. We don't need them because there is a difference between verbs which, translated to English, have the same meaning, and that difference is duration.
Sesti means to sit down. "pthalo's notebook" is the aim of that motion. That's why we need accusative.
Sedeti means to be sitting. Locative is used. Sitting is not a motion, it's position now.
It sounds really complicated, I'm sure , but for native speakers it's normal...
And i think it would be "FejliČinu/FejliČinoj"... but it's not that important.
You wrote "dvanaest godine", and it's logical... but we say "dvanaest godinA". There are two plural forms when you mention number of things.
1 godinA (singular)
2 godinE (plural)
3 godinE
4 godinE
5 godinA (plural- genitive)
6 godinA
...
11 godinA (plural- genitive)
12 godinA
13 godinA
14 godinA
15 godinA
...
21 godinA (singular)
22 godinE (plural)
23 godinE
24 godinE
25 godinA (plural- genitive)
26 godinA
...
As you see... 5 is an important number... it's a barrier between normal plural and its genitive form. And i find using singular for numbers 21, 31, 41, 101, 201, 1001... very interesting. We say "1001 noć", "101 dalmatinac" hehe.. and so on
It's reč, not reć... but i'm sure it's just lapsus calami.
And about your question... Many native speakers don't see difference between "umeti" and "znati"... "Znati" usually means to know something completely, but people say "Znam engleski" although they don't know it (completely). People usually say "Znam engleski" instead of "Govorim engleski", although the difference between those two could be huge. Anyway, everybody accepts that "Znati jezik" version. You can express different degrees of knowledge using different verbs.. (I'll try to remember some examples).
I always go into details... I don't know if it's good or bad.
Anyway I hope these information will be useful.