One must recite Shema with great kavana, with fear, awe, trembling, and sweat; she should contemplate in her heart that she is now reciting God’s word and focus on its meaning, as if they were new to her (SA 61:1-2).
In addition to kavana, one must pronounce the words of Shema precisely, taking care not to slur any letter, harden soft sounds, or soften hard ones. Therefore, le-khatĥila, one should distinguish between an alef and an ayin, a khaf and a ĥet, a kamatz and a pataĥ, and a tzeirei and a segol (SA 61:14-23). The Sages say, “If one recites Shema and is careful to pronounce its letters exactly, Hell is cooled for him” (Berakhot 15b). Be-di’avad, if she did not recite Shema meticulously, she nevertheless fulfilled her obligation as long as she did not miss a word or a full syllable (SA 62:1; MB 1).
One must hear what she is saying. Be-di’avad, if she read the words only with her lips but did not hear herself, since she mouthed the words, she fulfilled her obligation. However, one who only recited Shema in her mind, without mouthing the words, did not fulfill her obligation (SA 62:3).
Technically, one fulfills the mitzva by reciting Shema or the Amida in any language she understands, though it is proper to recite them in Hebrew (see above, 1:10). However, several major Aĥaronim write that nowadays one cannot fulfill the obligation by reciting Shema in a different language, because there are words that cannot be translated accurately. For example, the Hebrew word “ve-shinantam” (“teach them”) connotes both repetition (shinun) and sharpening (ĥidud). No foreign word captures exactly these meanings. Since the Shema cannot be translated precisely, there is no option to recite it in a different language (MB 62:3; see also Peninei Halakha: Prayer, ch. 15 n. 7).