You can use Levenshtein Distance, Jaro-Winkler Distance or Jaccard Similarity for that. You also find these measures ready implemented for most programing languages (e.g. Jellyfish for python or DKPro Similarity for Java)
Thank you for the answer but these distance metrics won't diffrenciate these two examples:
EcoleÉcole vs. helpheld
Both cases have the same distance with these simple distance metrics. I was looking for a method to have less distance to the first one rather than the second.