"It contains the Menology." What is the "Menology?" This implies it contains a service book, even tohugh it's a manuscript? Please clarify. Also, you have a lot of short sentences and paragraphs in here, this is discouraged in the GA criteria, it makes the article harder to navigate, with information everywhere.

"Paleographically it has been assigned to the 10th century" Does this mean it was written in the 10th century? Please clarify.

Instead of "It uses breathings (rough breathing, smooth breathing)" It would make the article much easier to understand if you just wrote "It uses rough and smooth breathings" Or something along those lines.

"It has subscriptions." what are subscriptions? I would suggest wiki linking this to the relevant article.

"In Genesis 12:4 it reads θεος for Κυριος" Isn't this information slightly random? Why is this important? Instead of just the vague section heading of "description" maybe you could use a level 2 heading to divide up your information, instead of just leaving spaces everywhere.

"The manuscript was brought from Syria in the 11th century" Who brought it? Why? Where did they bring it? Please clarify this information.

"The nomina sacra and other words are written in an abbreviated way" This is hard to understand. Don't you mean "Words such as "nomina sacra" are abbreviated" This would make the article more clear.

"The following words are abbreviated: και, πατηρ, μητηρ, υιος, θυγατηρ, ανθρωπος, Θεος, Κυριος, σωτηρ, πνευμα, ουρανος, Αβρααμ, Δαυιδ, Χριστος, Ιερουσαλημ" What do these words mean? Why are they abbreviated? Couldn't you re word this to make it more clear and use less examples by maybe writing "Some words in the manuscript are abbreviated. For example, και (give the meaning), πατηρ (give the meaning), μητηρ (give the meaning etc...), υιος, θυγατηρ, ανθρωπος, Θεος, Κυριος, σωτηρ, πνευμα, ουρανος, Αβρααμ, Δαυιδ, Χριστος, Ιερουσαλημ

"The error of itacism occur frequently: αι and η for ε, ει for ι, ω for ο, υ for οι." This is very hard to understand. I would suggest re writing it as "The error of itacism occur frequently, for example: αι and η are commonly mistaken for ε and ει is commonly mistaken for ι. Also, could you possibly explain what these mean?

"It contains the decorated headpieces, decorated initial letters, and musical notes in red at the margin" Why do you need the word "the" in there? It would read much better if you wrote "It contains decorated headpieces, decorated initial letters and musical notes in red in the margin" Is this what you mean? Where else do these features occur in the manuscript?

"Currently the codex is located in the Domschatz" What is "the Domschatz?" Also, what does "(Hs. 72, fol. 2-9)" mean? Could it be clarified?

Ref 3: What language is this in? Do you have a URL to the google books result for example or something similar?