English and every other language devolve into their old forms as you travel back through the centuries. Clearly, time travelers from the 22nd century or later have top-flight Universal Translation devices. These are discreet artificially intelligent gizmos that allow time travelers to understand and speak all languages known throughout history. Early versions hear spoken words and translate them into an earpiece or even show the translation in a hologram projected in front of the eyes like a TelePrompter only the wearer can see. Later versions playback a persons speech in a language the traveler understands within a microscopic earpiece. Then their spoken language is shielded by a series of nanobotic white noise speakers that also shoot forth what is said in the native language using the proper accent. All the while keeping with the natural sound of the user’s voice. Later centuries utilize holographic correction to the lips so the translated words match facial movements. These devices are also used in the future to speak with various extraterrestrial races as we colonize the Milky Way Galaxy and beyond!
The 21st century saw rudimentary versions of language translation that aren’t easy to use nor hidden from natives of the past. Those of us who are time travelers from the 21st century, 20th, or even earlier have been known to master a variety of languages but it becomes impossible the further back in the past you go. As far as English it becomes extremely difficult to understand what someone is saying before the 16th century. Some risk temporal law enforcement agents and steal translation tech from the future. Others in the world of the supernatural rely on witches and other practitioners of magic to cast miraculous spells or conjure up amazing potions that use metaphysical energies to translate language. In some cases, people are able to tap into their other selves in past lives and Parallel Universes where they are masters of a given language. Ultimately old school time travelers look to keep their head down and blend into a crowd having as little personal contact with anyone as possible. They’re in the past or future to complete a mission or simply observe history for their own enrichment or entertainment. Either way, they need to be ready to make a quick getaway once they are branded a foreigner in a hostile land or even worse a Devil speaking in tongues!