So this may be an odd question but I am of Eastern European descent so for me Slavic names resonate the best. My characters tend to have characteristics of their names and their meanings. I am living in the USA and write all my stories in English but I worry if readers will be able to identify with foreign names. Now they are not all direct Slavic names, some I make up but they all tend to be rather strong or in some peoples opinions harsh names. I know it is a silly question but I mainly have only had family and friends review my stories (they are all Eastern European too) and they say they work well but again that ethnic group is not my only audience for my stories (hopefully). Sorry for such a silly question and thank you.
Can you possibly give an example? Some names might indeed sound harsh and have stereotypes attached to them to different ethnic groups. If you're concerned about making the names universal, then, well, you can always pick some universal names... Michael, Helen, things like that.
are you concerned about first names, or family names? we need to see some examples if you want an opinion...
This may also depend to an extent on genre -- if you're writing fantasy, which tends to have more unusual names, it's less of an issue than if you're trying to write a contemporary story set in a suburban middle school. An easy way to fix this is via Find and Replace. Go ahead and use the names you want. After you've written your story and are satisfied with it, you can use your word processing feature to replace all "Kasimir"s with "Connor" or whatever name seems to fit more with the age of your characters and their world. However, you might be okay with keeping them as they are. You could make the family of your MC Slavic and that could work very nicely to give them a specific identity and enable you to put in some cultural flavor that could enrich your story. Some Slavic names are not really that uncommon or are very close to names from other origins that wouldn't necessarily strike someone as unusual.
Your characters' names should fit the setting or their individual background. So, if your story isn't set in a Slavic country or a city/town with a large Slavic population Slavic names will seem out of place. You may want to browse some naming sites (behindthename.com is a personal favorite of mine but, sadly, it won't help you on last names) to see what names are popular in what countries and use this when worldbuilding. It's just as much of an issue there. Even when writing fantasy or science fiction, names (should) follow patterns. Characters from "Country X" will have different naming conventions from those in "Country Y" (unless the two places are virtually the same). Names are influenced by culture and a person's name can give hints of that person's parentage, nationality, or even their religious beliefs. It's one of those sweet spots where worldbuilding and character development meet.