How can a foreigner know?

How can a foreigner know how to say: "I present all present with this present." that is, when he sees it in writing. All right, all right, so nobody would dream of using this phrase but, just for the fun of it. How would you show him the right way. Remember you're supposed to be mute, can't help orally, only in writing. In Greek, no problem, you put a diacritical (lovely word) mark on the spot you want stressed. You could use capital letters to mark stress:
I preSENT all PREsent with this PREsent.

Or you could, like the Greek, or the Spanish, Portuguese and others, use accents. No, not like the French, they use accents for sound only, not for stress. No need in French, all words are always stressed on the last syllable, no exceptions. Now try that silly phrase of mine with accents:
I presént all présent with this présent.

In ancient Greek it's just been taken a step further and nearly all words carry a written accent (want to see the exceptions?). So as to make sure everybody knows what's what.
Lét's dó the sáme wíth Énglish. Áll wórds nícely spélt, wíth diacrítical márks ánd áll.

Ó, Ì neárly forgòt tò úse the gráve áccent òn wòrds fóllowed by óthers (ops, the y shoúld táke a gráve bùt refúses tò dò só òn my (agaìn) kéyboard, yoù jùst háve tò imágine ít).

Now for the long circumflex: We could write - but don't - mâster, long stressed a (- macron for long, and ´ stress all in one), âfter, áftershave (longish, but not as long as in âfter, unless we want to sound short-of-breath husky and râther stránge). Beaûty but beaútiful. Try it.
English is not all that different from Greek in that we try to say things the easiest possible way.
Real ancient Greek was written all in capital letters, without diacritics, and also without punctuation marks. Do you think that would be easier to read out loud? Try it!
If you don't intend to read ancient Greek out loud, don't waste your time on accents, learn something else that really interest you. But it is much easier to remember words if you know how they are said, and that is where a little knowledge of accents comes in very handy indeed.