Can someone explain why this is talking about one singular thumb, as opposed to thumbs (plural) when it is मेरे अंगूठे and not मेरा अँगूठा ?
मेरे अंगूठे is the oblique case form of मेरा अंगूठा. The oblique case is needed with the postposition में.
The plural oblique form is actually अंगूठों (aṅgūṭhõ) – although I'm guilty of confusing the dependent forms of ऎ and ओ every now and then myself too.
I don't like the way the English solution has been constructed here. The translation should just be literal: my thumb is in pain (or in the least accepted as an alternative translation). The Hindi sentence doesn't contain any of the words that might translate to "there"
Additionally, with the Hindi SOV structure, isn't "my thumb" the subject? Therefore that should remain the subject in the translation
There is no object in this sentence. मेरे अँगूठे में (in my thumb) is an adverbial, it is neither an object nor a subject. The order here is Adverbial + Subject + Verb.
There are no direct translations in any language that I am aware of; In English, we'd say "My thumb hurts".