As I’m not a native English speaker I feel particularly qualified to answer this haha… my perspective is based on what I know of Indo-European languages and popularity statistics in Europe and different non-native accents in English.
[name_f]Eleanor[/name_f] - Looks confusing, but once you know how it’s pronounced I think most people can quite easily manage.
[name_f]Martha[/name_f] nn [name_u]Mattie[/name_u] - ‘th’ is perhaps the most difficult sound to produce for non-native English speakers, while as a pp said Castilian Spanish speakers will absolutely nail this sound even though most Spanish [name_f]Martha[/name_f]'s I believe are called [name_f]Marta[/name_f] with a clear ‘t’ sound, this is not a given for many others.
[name_f]Claire[/name_f] - Quite English/[name_m]French[/name_m]-ish in terms of style, so in that sense not truly multicultural, but like [name_f]Eleanor[/name_f] once you know how you’re expected to pronounce it, it’s quite easy.
[name_u]Evelyn[/name_u] nn [name_f]Evey[/name_f] - This name confuses me more than it probably should, I believe even within Anglophone countries there are discussions as to how it’s supposed to be pronounced. Other than that the likes of [name_f]Eveline[/name_f] and [name_f]Evelina[/name_f] are fairly multicultural.
[name_f]Margaret[/name_f] nn [name_f]Margot[/name_f] - This is one of those names for which most languages have their own alternatives, so in this form it’s very very English, not the most difficult to pronounce but maybe not as multicultural as you would like
[name_u]Meredith[/name_u] - As I said before, ‘th’ is a challenge, but ‘th’ at the end of a word or name is impossible for many. I’ve been told I don’t really have an audible non-native accent when speaking English, but on my ‘bad English days’ this name is impossible for me too.
[name_f]Isla[/name_f] - Very easy once you know, very very very confusing on paper, and I believe it’s also the Spanish word for ‘island’?
[name_f]Ada[/name_f] - This one works well in many Indo-European languages.
[name_f]Josephine[/name_f] - Might be even safer with an ‘f’ instead of ‘ph’, but it’s one of the most recognisable ones.
[name_f]Nora[/name_f] - Very easy, very multicultural.
[name_f]Miriam[/name_f] - Once again, I think this works well in many/most Indo-European languages
[name_f]Olive[/name_f] - word name, [name_f]Olivia[/name_f] works a charm, this might not.
[name_f]Iris[/name_f] - Could work, if you’re willing to accept vastly different pronunciations.
[name_u]June[/name_u] - On a ‘bad English day’ this is Joon to me, and for many others. The different type of ‘oo’ sounds in English are really quite challenging to distinguish and many non-native speakers don’t detect the difference and therefore also won’t pronounce/can’t pronounce this name as you might like. Otherwise it’s actually quite easy and straight forward.
[name_f]Sophia[/name_f] - Very multicultural, especially if you spell it with an ‘f’
[name_f]Daisy[/name_f] - [name_m]Even[/name_m] though it’s clearly English, it is quite easy to pronounce.
[name_u]August[/name_u] - This is quite international once you accept the different pronunciations.
[name_m]Samson[/name_m] - Pretty international
[name_m]Declan[/name_m] - Despite its being Celtic and therefore somewhat tied to Anglophone countries, I think this might be pretty doable actually but it’s not truly international.
[name_m]Ethan[/name_m] - It’s apparently popular in [name_f]France[/name_f] these days, but I don’t think they pronounce it the way they would in English, it’s that ‘th’ again…
[name_m]Conrad[/name_m] - Expect different pronunciations otherwise you’re good to go with this one.
[name_m]Leo[/name_m] - This is very international in that it is one of the most trendy names in different European countries at the moment if recent statistics are anything to go by, but do expect different pronunciations.
[name_m]Oliver[/name_m] - I think this name works suprisingly well across different European countries
[name_m]Theodore[/name_m] - Actually quite trendy in several countries in Europe as well, but there’s the ‘th’ again so once again you can expect the hard T sound rather than ‘Th’.
[name_u]Elias[/name_u] - Works well, but do expect different pronunciations.
[name_m]Ezra[/name_m] - I think this one works well too.
[name_m]Charles[/name_m] - I always struggle a bit with this name, basically the ‘rls’ sound is a challenge because it requires a different ‘r’ than I am used to and a different ‘s’ than I am used to, which actually borders on an ‘sh’ sound to many Anglophone ears.
[name_m]Henry[/name_m] - Quite international, or well European, if you accept different pronunciations.
Many of the more international names that feature on many popularity statistics in countries where an Indo-European language is spoken or predominant have been around for centuries basically so some might be a bit stale. In my recent random survey of different popularity statistics in Europe, these names were going around quite a lot: [name_f]Maria[/name_f], [name_f]Clara[/name_f], [name_f]Lara[/name_f], [name_f]Emilia[/name_f], [name_f]Emma[/name_f], [name_f]Alina[/name_f], [name_f]Lina[/name_f], [name_f]Lena[/name_f], [name_f]Laura[/name_f], [name_m]Oscar[/name_m], [name_m]Leon[/name_m], [name_m]Lucas[/name_m], [name_m]Ruben[/name_m], [name_f]Nora[/name_f], [name_f]Sara[/name_f], [name_f]Alice[/name_f], [name_f]Alicia[/name_f], [name_f]Sofia[/name_f], [name_m]Matthias[/name_m]/[name_m]Mathis[/name_m]/[name_m]Matteo[/name_m] etc. etc., [name_m]Casper[/name_m], [name_f]Louise[/name_f], [name_f]Elise[/name_f], [name_f]Elena[/name_f]…