| Imma | | - | Italian, Catalan | |
| Immaculada | | - | Catalan | |
| JÚLia | | ZHOO-lyə (Portuguese), YOO-lee-aw (Hungarian) | Portuguese, Catalan, Hungarian, Slovak | |
| Jan (1) | | YAHN (Dutch, Swedish, Norwegian, Polish, German) | Dutch, Swedish, Norwegian, Danish, Czech, Polish, Slovene, German, Catalan | |
| Jana (1) | | YAH-nah (Dutch, German) | Czech, Slovak, Dutch, German, Slovene, Catalan | |
| Jaume | | ZHOW-mə | Catalan | |
| Jaumet | | - | Catalan | |
| Joan (2) | | joo-AHN (Catalan), zhoo-AHN (Catalan) | Catalan, Occitan | |
| Joana | | - | Portuguese, Catalan | |
| Joaquim | | - | Portuguese, Catalan | |
| Joaquima | | - | Catalan | |
| Jordi | | - | Catalan | |
| Josep | | - | Catalan | |
| LÍDia | | LEE-dyə (Portuguese), LEE-jyə (Brazilian Portuguese) | Portuguese, Catalan, Hungarian | |
| Laia | | LAH-yə | Catalan | |