These pages have links that your daughter might enjoy:

https://www.hoagiesgifted.org/language.htm

https://www.hoagiesgifted.org/books_authors.htm

Your DC might enjoy Madlibs.

As a child, I loved the Schoolhouse Rock songs, but my kids weren't into them.

I agree with PPs that writing on her own might be good. If she writes a story or a poetry collection, you can have it bound in a book. (Illustory)

The Folger Library has an annual celebration of Shakespeare's birthday (in the spring). There are lots of activities and crafts.

I agree that reading is probably the best way to supplement. Depending on her reading levels and interests, you might try classics or books that feature wordplay/puns.

Elementary school in general is sadly rather lacking in rigor, OP, even the little 4th-5th grade magnets. It gets more interesting in middle and high school, I promise
In the meantime, enrich at home.

There's not really English in MCPS ES unless you're talking about ESOL, which I assume you're not (if you are, request that he be removed from the program--there's a form you can sign, and he will be reassigned "level 10" and not receive services).

If you mean English as in reading, then supplement" by encouraging him to read books on his own that interest him, and have conversations with him about what he's reading, what he thinks might happen next, what does he think of the characters, etc etc.

If you mean English as in writing, there's always more and more detail he can add to his writing. Get a blank journal for him and encourage him to write during his down time. You can find prompts online, or just let him free write about whatever's on his mind. You can write letters back and forth to each other, etc.

I would bring it up at conference time with the teacher and take a look at his work. Maybe it's "too easy" because he's not trying his best and is capable of doing more.

Have you seen his work? I would want to know either from the teacher or by seeing it if he is putting in effort or just doing something minimal and complaining.

Is your child allowed to read when they have completed the class assignment? There are almost always ways to add more detail to both pictures and written work. I'm pretty sure my older DD read through large portions of the language blocks in 2-3 grades.

What are they doing? English seems like something that easily adapts to any level a child is at. One kid is drawing a picture with two words under it. Another kid is writing a paragraph.

My dd actually liked it when I would give her a writing prompt that required her to do a little research, reach a conclusion, and then write an essay. She asks me to do this over summer break. We’d sit down and talk about how to make the meaning of a particular sentence more clear to the reader or how to say something more concisely. We’d go over the punctuation. Also, help your child find books that are really engaging for him/her. As long as the book is age appropriate, don’t place any limitations on the subject matter. Try to expose dc to different literary genres. Talk about what makes him/her like a particular author. Invite dc to write a couple original paragraphs in the style of dc’s favorite author.

Our DC is complaining that English class in 2nd grade is too easy, even the advanced level. Any suggestions for supplementing outside of class, such as workbooks or classes in language arts?
Thanks!