| Johanne | | zho-AN (French), yo-HAHN-ne (Danish) | French, Danish, Norwegian, Medieval French | |
| Josse | | - | French (Rare), Medieval French | |
| Judd | | JUD (English) | English, Medieval English | |
| Jurian | | - | Medieval Low German | |
| Kazimir | | kah-zee-MEER (Russian) | Russian, Medieval Slavic | |
| Kinborough | | - | Medieval English | |
| Krasimir | | - | Bulgarian, Medieval Slavic | |
| Kresimir | | - | Medieval Slavic | |
| Kyrilu | | - | Medieval Slavic | |
| Larkin | | LAHR-kin | Medieval English | |
| Law | | - | Medieval English | |
| Lorencio | | lo-REN-thyo (Spanish), lo-REN-syo (Latin American Spanish) | Medieval Spanish | |
| Lyubomir | | - | Bulgarian, Medieval Slavic | |
| Lyudmil | | - | Bulgarian, Medieval Slavic | |
| Lyudmila | | lyood-MEE-lah (Russian) | Russian, Bulgarian, Medieval Slavic | |