Index: logback-core/src/main/java/ch/qos/logback/core/util/CharSequenceToRegexMapper.java
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- logback-core/src/main/java/ch/qos/logback/core/util/CharSequenceToRegexMapper.java	(revision be4334e9697ae6435a2c2ad3099007b7cb51e612)
+++ logback-core/src/main/java/ch/qos/logback/core/util/CharSequenceToRegexMapper.java	(revision )
@@ -59,7 +59,7 @@
           return getRegexForShortDaysOfTheWeek();
         }
       case 'a':
-        return ".{2}";
+        return getRegexForAmPms();
       case 'Z':
         return "(\\+|-)\\d{4}";
       case '.':
@@ -80,6 +80,11 @@
     }
   }
 
+  private String getRegexForAmPms() {
+    String[] amPms = symbols.getAmPmStrings();
+    int[] minMax = findMinMaxLengthsInSymbols(amPms);
+    return ".{" + minMax[0] + "," + minMax[1] + "}";
+  }
 
   private String getRegexForLongDaysOfTheWeek() {
     String[] shortMonths = symbols.getWeekdays();
Index: logback-core/src/test/java/ch/qos/logback/core/util/DatePatternToRegexTest.java
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- logback-core/src/test/java/ch/qos/logback/core/util/DatePatternToRegexTest.java	(revision be4334e9697ae6435a2c2ad3099007b7cb51e612)
+++ logback-core/src/test/java/ch/qos/logback/core/util/DatePatternToRegexTest.java	(revision )
@@ -96,7 +96,12 @@
   @Test
   public void amPm() {
     doTest("yyyy-MM-dd a", CAL_2009_08_3_NIGHT);
+    doTest("yyyy-MM-dd a", CAL_2009_08_3_NIGHT, CZ_LOCALE);
+    doTest("yyyy-MM-dd a", CAL_2009_08_3_NIGHT, KO_LOCALE);
+
     doTest("yyyy-MM-dd a", CAL_2009_08_3_MORNING);
+    doTest("yyyy-MM-dd a", CAL_2009_08_3_MORNING, CZ_LOCALE);
+    doTest("yyyy-MM-dd a", CAL_2009_08_3_MORNING, KO_LOCALE);
   }
 
   void doTest(String datePattern, Calendar calendar) {