The provided source material does not contain information regarding a city named Wasla in Nicaragua. Instead, it describes "waṣla" (or hamzatu l-waṣli) as a linguistic and orthographic term used in Arabic script.
In grammar, the waṣla is a variant of the letter hamza that resembles part of the letter ṣād. It is sometimes placed over the letter ʾalif at the beginning of a word to indicate that the alif is not pronounced as a glottal stop because the word is connected to the preceding one. Outside of vocalised liturgical texts, the waṣla is typically not written.