It is certainly acceptable, although some publications have diacritics as part of their house style, and if the author doesn't use them, the copy editor is supposed to insert them.
The New Yorker writing things like coöperate and reëlect is probably the most infamous, although they are not the only ones.
The Guardian style guide says to use spellings exposé, lamé, résumé, and roué – but not café. Although, when giving the name of an organisation/institution (restaurants and cafés included), the article should use whatever spelling is preferred by the management, including their choice about how to spell cafe/café (when that word is part of their name).
Personally, I'd always write café in formal English, because cafe just looks wrong to me. However, in something informal like a text message I probably wouldn't bother.
Sure, some publications might like that. And some publications still treat data as a plural of datum rather than a mass noun like water. But I don't think I know a native speaker who would look at "naive" and feel the way they do when thy see "could of".
The New Yorker writing things like coöperate and reëlect is probably the most infamous, although they are not the only ones.
The Guardian style guide says to use spellings exposé, lamé, résumé, and roué – but not café. Although, when giving the name of an organisation/institution (restaurants and cafés included), the article should use whatever spelling is preferred by the management, including their choice about how to spell cafe/café (when that word is part of their name).
Personally, I'd always write café in formal English, because cafe just looks wrong to me. However, in something informal like a text message I probably wouldn't bother.