“Hear, O Israel.”
There are two aspects to the mitzvah of the Keriat Shema. First, we are supposed to recite it, morning and night. That’s what keriah means: recite this Torah passage aloud. And, we are supposed to absorb its message. That’s what shema means: we are called upon to hear.
Jewish tradition has always insisted on interpreting the Torah in precise and concrete ways that produce specific behaviors and legal norms. We don’t generally like misty metaphor alone; we generally prefer to turn metaphors into norms of how to live.
The word שמע/shema/hear is no different. The ancient Sages sought specific legal meanings in this word. What does it tell us to do?
First, it means that you should say the words audibly. Don’t think the Shema. Speak it. Halakhically [or “in Jewish law”], you absolutely must move your lips as you say the words. Ideally you should also speak loudly enough that you can hear yourself; but if you whisper so softly that you cannot even hear yourself … well, that’s not great, but it’s acceptable.[See all that in the Talmud Berakhot 15a and Shulhan Arukh Orach Hayim62.3.]
Another interpretation: in idiomatic Hebrew שמע/“hear” can also mean “understand,” in addition to “perceive sounds.” We say this in English, too: “I see your point” or “I hear what you’re saying.” Employing this usage, the Talmud offers this interpretation: שמע – בכל לשון שאתה שומע
“Shema means: it can be said in any language you understand.” [See Mishnah Sotah 7.1, and on the aforementioned Talmud page, and ShulhanArukh OH 62.2.] This rule applies also to the Amidah or most ritual blessings, by the way.
It is always considered optimal to recite in Hebrew, the language we inherited from our ancestors and share with Jews worldwide. The Shema is a text from the Torah, after all. And so Hebrew is always recommended, even if you don’t understand all the words.
But Judaism has generally viewed translation positively, as “bringing the beauty of Greece into Jewish tents,” as the Midrash says. So reciting Shema in translation is absolutely kosher. This rule applies only to languages you personally understand: I can recite in English, but not Hungarian or Japanese. Certainly there can be nuance and beauty that is “lost in translation,” so I do think Hebrew is best. But maybe some spiritual experience can be “found in translation” too. So I encourage you sometimes to trot out your English (or Portuguese, Italian, Russian …) and bring it to shul. Maybe it will help you “Hear, O Israel.”