An easy approach to your problem could be to use the .replaceAll(String regex, String replacement)
method available in the string class. This would allow you to replace all instances which match the given regular expression. Thus, the code below:
String input = "Løre lære i kjøpe";
String result = input.replaceAll("ø", "oo");
result = result.replaceAll("æ", "ae");
System.out.println(result);
Would yield:
Loore laere i kjoope
Thus, you could have a method which processes the text through a series of replace calls. You could add some intelligence to it and allow it to also replace capitalized words with their English equivalent.
If you have a lot of them, you could create a configuration file which your application then loads in a Map
like structure. You could then iterate over the map and use it to replace chunks of text from your source string.