Have there been any studies about the benefits of reading aloud for language acquisition?
There are several that I can think of:
Most notably, reading out loud allows you to improve your pronunciation of the language. This can help you identify sounds or accents you're having trouble with in the language.
Reading out loud allows helps you feel more fluent while speaking with a native speaker. You will feel more confident when having a real conversation if you practice by reading out loud, even if you're simply just repeating words from a a page.
Finally, I'd argue that in certain cases, reading out loud can allow you to better understand the meaning of any words that you might not understand. Verbal repetition has a way of cementing the meaning of any words you might not know and revealing the words you don't know the definition of.
Keep in mind that is all from my own personal experience though.
I'm not sure about studies, but there are a few polyglots who have commented on the usefulness of reading aloud.
Olly Richards explains in his YouTube video Is reading aloud a helpful language activity? (September 2016) that reading aloud is not useful as a study method, except for practising pronunciation and intonation. As a pronunciation exercise, it is most useful if you can get feedback on your pronunciation.
However, reading aloud is an uncreative use of language, unlike conversation or preparing a speech (and rehearsing it!). When reading aloud, you tend to focus on the pronunciation and intonation that it is difficult to take in the content of what you are reading.
Vladimir Skultety explains in his video Random language learning tip #2 | Read out loud (August 2015) that reading out loud trains the muscles in your mouth that you need for pronouncing the sounds of the language. He says that the effect is not so big if you do it only for a few minutes; you will improve when you do it 15 to 30 minutes each time. By reading out loud, you practice pronouncing sounds that you are not used. The muscle memory that you develop this way should help you improve your pronunciation.
Outside of language learning, Patrick King claims that you can use it to improve your social skills. Each day, you should read 400-500 words, emphasizing the feelings, the emotions, the reactions and the dialogue "to the tenth degree". This should have several benefits: it should "improve your vocal projections", improve your enunciation (which is what Olly Richards and Vladimir Skultety also said), teach you how to breathe properly, teach you how to "accurately convey emotional highs and lows", and make you comfortable with your voice. You should see benefits after doing this each day for fourteen days.