It depends entirely on how you are encountering this person (long-distance or in-person), whether you share languages or have some degree of mutual intelligibility, and whether you have a simple or complex idea to communicate.

Jerry V. Tobias has written:

'Massed versus distributed practice in learned improvement of speech intelligibility' -- subject(s): Intelligibility of Speech, Research, Speech, Intelligibility of

Yes.

If only one person understood a language, then it would not be a language because language by default needs to facilitate communication. Urdu is one of the most popular first-languages in the world.

If your question was asking if there mutual intelligibility between Urdu, Hindi, Gujarati, and Marathi, there is a high degree of mutual intelligibility and more worldly speakers of any of these four can typically figure out what is said in any of the other three, but in order to have a more serious conversation, they would need to speak the same language.

Intelligibility is a non-count noun, so there is no plural form.

Another example of a non-count noun is understandable. Because you can not count understandable it will never appear in a plural form (understandables).

Ultrasound can be perceived through bone conduction by the profoundly deaf as well as by normal-hearing subjects. Moreover, speech signals modulated onto ultrasound can be detected through bone conduction. This study explored how well listeners can understand ultrasonic speech and the confusion patterns to evaluate and improve bone-conducted ultrasonic hearing. The intelligibility of Japanese words classified by familiarity and Japanese monosyllables with bone-conducted ultrasound was investigated. Results showed that the intelligibility of familiar words was higher than that of unfamiliar words. Further, the results of a monosyllable intelligibility test with bone-conducted ultrasound and those of a test with air-conducted sound showed a similar pattern of speech recognition with regard to the errors made. The relationship between speech intelligibility and sound level showed that the increase in the intelligibility of bone-conducted ultrasonic speech did not exceed the increase in the intelligibility of air-conducted speech as the sound level rose.