IJPL-194260 Umlauts in code names cause spellchecker false positive

Merge-request: IJ-MR-167314
Merged-by: Ilia Permiashkin <ilia.permiashkin@jetbrains.com>

GitOrigin-RevId: 8b35392555b59cf4c94e8767acdb46218fe57668

plugins/kotlin/idea/tests/test/org/jetbrains/kotlin/idea/grazie/KotlinGrazieSupportTest.kt

@@ -28,6 +28,10 @@ class KotlinGrazieSupportTest28 : GrazieTestBase() {
         runHighlightTestForFile("grazie/StringLiterals.kt")
     }
 
+    fun `test umlauts doesn't produce false positives`() {
+        runHighlightTestForFile("grazie/Umlauts.kt")
+    }
+
     fun `test text extraction in string literals`() {
         val file = myFixture.configureByText("a.kt", "val s = \"foo $" + "{injection} bar\" ")
         val content = TextExtractor.findTextAt(file, 10, TextContent.TextDomain.ALL)

plugins/kotlin/idea/tests/testData/grazie/Umlauts.kt

@@ -0,0 +1,5 @@
+package ide.language.kotlin
+
+fun `ähnliche Werte sollen gruppiert werden`() {
+
+}

spellchecker/src/com/intellij/spellchecker/inspections/IdentifierSplitter.java

@@ -20,7 +20,7 @@ public class IdentifierSplitter extends BaseSplitter {
     return INSTANCE;
   }
 
-  private static final @NonNls Pattern WORD = Pattern.compile("\\b\\p{L}*'?\\p{L}*");
+  private static final @NonNls Pattern WORD = Pattern.compile("(?U)\\b\\p{L}*'?\\p{L}*");
   private static final @NonNls Pattern WORD_IN_QUOTES = Pattern.compile("'([^']*)'");
 
   @Override