Must the hagada be read in hebrew? Or in whatever native language one knows (if they do not know hebrew)?
Shalom, Thank you for your question. Apart from the mitzvah of eating matza, bitter herbs, and drinking the four cups, Seder night is also the night we fulfill the command to tell the story of the Exodus from Egypt. This mitzvah is so important that we go to great lengths to make sure that all he children (and adults) will take part – everything from stealing the afikoman to singing together Chad Gadyah. We certainly need to make sure that everyone understands what is being said. Because of this, the halacha is that one should indeed say the Hagadah in a language that those taking part in the Seder will understand. In fact, the Shulchan Aruch (Orach Haim, 473,6) records "And one should recite [the Hagadah] in a language that the women and children will understand, or [at least] explain to them the ideas. This was the practice of R[abbi] I[saac] from London, who would recite the whole Hagadah in [his local] language, in order that the women and children would understand". (The need to translate especially for women applied in past when women lacked high level Torah education, and often did not understand Hebrew. Today of course there is no difference in this matter between men and women – either they know Hebrew or don't). So, in answer to your question, one should certainly make sure that all those around the Seder table either have access to a Hagadah with a translation they can read, or one should translate (or explain) to them what is being said. It is also acceptable to forgo the Hebrew entirely, and just recite from a translation. However, in such a case, it would be better if at least the Blessings were recited in Hebrew (Kiddush, Grace after Meals, the blessings on hand washing, matzah, marror etc). [This is because there is some disagreement as to exactly how to translate these Blessings, and an invalid translation may invalidate the blessing]. But, if needed, then even the blessings may be recited in translation. (I have seen in some translations where they do not use the word "G-d", but rather "Hashem" – if the blessing is being recited at the Seder in English one must say "G-d" or "Adonai" and not just say "Hashem"). The most important parts to translate are the sections where Rabbi Gamliel says "He who does not say three things on Passover night does not fulfill their obligation – Pesach, Matzah and Marror", and the three paragraphs that follow explaining each of these items. It would correct to also translate the Ten Plagues, and explain them. Beyond these sections it is up to you – but, in the words of the Hagadah "the more one tells over of the story of the Exodus, the more praiseworthy it is". May you be blessed with a wonderful and holy Seder night!