The English context provided is somewhat ambiguous. If we take the word "periodical" out, the sentence will read just fine, with "monthly workshops" as a plural subject, and the verb "offer" will then agree with the subject in number. The same will be true if the word "periodical" is retained, but understood as an adjective, followed by the more specific adjective "monthly." In this case, the word "periodical" would be superfluous, as anything that is monthly will also be periodical.

The last two answers, however, see the sentence differently, with the word "periodical" understood as a noun, and "monthly workshops" as the name of the periodical. If this is correct, one would expect the words "Monthly Workshops" to begin with capital letters and to be followed by a comma, and the verb "offer" to be "offers" so as to agree with the third-person singular subject.

The translation suggestion that I am offering will work regardless of how the word "periodical" is understood, but I am pointing out the ambiguity because you may be able to eliminate it with slight modifications to achieve greater clarity.

Fuad