Shouldn't StartWith and EndsWithcalls in other places be adjusted? To make sure FA is consistent on all OS/Cultures.
F.e. in the following files:

• CallerIdentifier.cs
• Execution/LateBoundTestFramework.cs
• Primitives/StringAssertions.cs
• Types/TypeSelector.cs

Agree.
We should also be explicit when using the following string methods, as not specifying a StringComparison defaults to StringComparison.CurrentCulture.

• StartsWith
• EndsWith
• IndexOf
• LastIndexOf
• Compare

I did originally do a full search and replace from StringComparison.CurrentCulture to StringComparison.Ordinal, but since there are no existing tests for culture-sensitive behavior and I'm not sure I can figure out the potential impact of changing it in each of the places mentioned by @eNeRGy164, I ended up only committing the changes in StringAssertions.

Should I go ahead with the full search and replace plus adding StringComparison.Ordinal to all the calls mentioned by @jnyrup?

@kimsey0 It would be an appreciated contribution if you would do the replacements/additions and succeed in adding culture aware tests. That should finally(!) give Fluent Assertions consistent and expected behaviour.
If you need other cultures besides Danish to test against, we have earlier fixed problems due to German and Polish cultures.

@kimsey0 How are things working out?
We're getting close to release 5.10.0, and it would be great to have this in.
Anything's blocking you or just lack of time?
Let me know if you need any help.

Just lack of time. How's your timeline on 5.10.0? When would you like to have this merged for it to ship with that release?

@kimsey0 We don't have a lot of progress from merging a PR to releasing a new version, so in practice in can be merged last minute.

I am hoping to release 5.10.0 this year.

Let's move this to 6.0. Hopefully @kimsey0 is willing to do the work @jnyrup requested.

@kimsey0 are you still up for it?