Shulchan Arukh Orach Chayim · Siman 62

English

[The Laws of] one who is not precise with the recitation of the Shema or did not make it heard to his [own] ears, and it contains 5 se'ifim Even though it is a mitzvah to be precise regarding the letters [of the Sh'ma], one who has recited it without being precise with them has [nonetheless] fulfilled their obligation.

English

One may read [the Sh'ma] in any language, and they should be careful to avoid word mispronunciations in that language, and one should be precise in it just as in Hebrew [lit. "the Holy tongue"].

English

[When reading the Shema,] one must hear with their ears what comes out of their mouth, but if one did not hear it, they [still] fulfilled their obligation as long as they brought it out of their lips (i.e. articulated it with their mouth).

English

If, due to illness or some other unavoidable circumstance, one recited the recitation of the Sh'ma in their heart [i.e. silently], they fulfilled their obligation. Rem"a: And even optimally one may do this if they are in a place which is not completely clean and they are not able to clean it up due to unavoidable circumstances, [in such a case,] one may think [it] in their heart (i.e. recite it silently to themselves) as long as the place is not completely soiled [e.g. with excrement] since it is forbidden to think a matter of Torah in a soiled place. (Beit Yosef, Siman 85)

English

The prayer-leader needs to make his voice heard with "Sh'ma Yisrael" so that the congregation will hear and declare the kingship of the Heavenly Name together.