I think it is, ex (French president) is a correct parsing of that phrase. French ex president is less specific because we then know their nationality but the speaker has left a large degree of ambiguity over what they were president of.

No, it isn't. It sounds like he's still the president, but he's no longer French.

Yet, it happens so often, one would think it was OK. Like the Salisbury poisoning, where the victims were referred to as an 'ex-Russian spy', when he was really a 'Russian ex-spy'. Unfortunately, there are cases, where if one is true to form, it becomes rather a mouthful.

Unfortunately, I believe it is because what they mean to say is he is no longer the French President (as if 'French President' was a single term), and attach 'ex-' in front of that term. Similarly for the 'Russian spy', which apparently is also a single term, rather than two terms.

The correct way to handle it is to use the word "former" instead. "Former French President" parses correctly.

"Ex-" binds tightly to the word in front of it because of the dash, but "former" allows "French President" to be the noun phrase being modified.

Only in your incredibly contrived interpretation of the english language. "Former" would be better here but there is still not any significant ambiguity as to what is meant.

It's clear what they meant to say, but that doesn't make it correct. Just because someone can understand me when I'm speaking broken Russian doesn't mean my grammar is suddenly good.

If it's clear what you're saying, then it is okay to say it. Nobody said anything about formal correctness until now.

Newspaper headlines ought to be formally correct.

If you have space, ex-president of France seems more precise.

French ex-president is a bit less clear. There’s a little ambiguity about what kind of president is being referenced, but the article should provide that context.

France has multiple kinds of presidents?

There are multiple presidents that are French.

Contrary to the US, when a president isn't president anymore we stop calling him "President" -- it's not a honorary title for life

Sure. Président is a common name for a group leader, and it's the French equivalent of CEO. So there are many possible French presidents.

"Renault sues French ex-President" would probably refer to Ghosn, not Hollande or Sarkozy.

ex-(french president) was what they were trying to say, but unfortunately that doesn't look good as a headline.

french ex-president doesn't sound right to me, because that would mean a french person who is an "ex-president". Subtle difference, but to make a point let me stretch it out a bit. He could be an "ex-president" of anything, maybe an ex-president of a high school class, and just happens to be a french guy.

What they're trying to say is a person who is an "ex-president of france", so the "ex" prefix applies to "french president".

It depends on whether he's bald