Ask The World

As an Egyptian, maybe a little over a thousand years, as that's when most people started speaking Arabic, though depending on where exactly I am I could luck into an Arab community, in which case I'd last until maybe 1200 years go. Before that it was Coptic and I don't speak a lick of that.

I wouldn't be confident going past the 19th century US, personally. English has changed a lot in a short time.

At least 500 years. I think the limit would be somewhere around 600-800, as that's when the language changed a lot due to foreign trade. I could probably get by in a pinch before 1300, provided everyone spoke really slowly. I don't speak Norse, but a lot of the words have carried over into my modern language.

Probably around 1800s around this time Philippines would still be under Spain most people would be talking Spanish language, people still speak their local languages but will probably be too deep compared to what we have now. Which has a lot of code switching. Around WW2 killed a lot of Spanish speaking people and most importantly publications that pretty much ended Spanish language in Philippines. Though it was already in decline to due USA directive to use English for everything, including education, present day though we still use borrowed words and some parts of the country even have a creole version of the Spanish language.

As an American, I'll include England, in which case, it's really longer than you'd think before you'd need a translator. Shakespeare gets a lot of guff, but it's important to remember he was writing in a elevated register and everyday vocabulary would be a little easier to parse. The accent itself wouldn't be that bad, a rhotic accent that hits my American ears with a combination of Cockney, West Country, and a sort of indistinct Irishness, but as David Crystal points out, because it predates much of the geographic splintering caused by the British Isles diaspora in the 17th through 19th centuries, Anglophones from all across the world often find some aspect of it that feels familiar.

Now, Chaucer was before the Great Vowel Shift really got going, so it's tougher, but I think if you found a motivated conversationalist, you'd adjust quickly enough to function without needing a formal translator. Chaucer influenced written English quite a bit, and he was speaking with a London accent that contributed more to current dialects than some others, so it might be impractical to go much earlier than him. The bigger issues than language itself would really be cultural context and general knowledge of the time and place.

https://en.wikipedia.org/wiki/Mikael_Agricola

Agricola's Finnish is reasonably understandable, so about as far as the records go. 1500's or so.

Maybe some linguist might have ideas about earlier history, but that's my guess.

A little over 500-700 years I think.