Based on Apex Court decision here, Single Judge of High Court of Tripura held that the evidence of a dumb witness is a competent witness as per section 119 of Evidence Act.

[14] Evidently the petitioner was produced in court and an expert trained in sign language was also engaged by the court to interpret her evidence. As observed by the court, since the petitioner did not understand sign language she could not communicate her evidence to the interpreter and as a result the interpreter could not interpret her evidence to court. However, the petitioner was able to communicate to the court by her signs and gestures that everything of her life was known to her mother.

[15] In this emerged situation, mother [PW-2] of the petitioner is the best witness on her side. She had intimate knowledge of the signs and gestures and meaning of all expressions of her daughter who was brought up by her since her birth. None on earth other than her could better understand her daughter. The mother categorically stated at the trial that marriage of her daughter with the respondent was solemnized in a temple at Kumarghat and after marriage a daughter was born to her and thereafter the respondent left the area. Her evidence was supported by PW-3, a 70 years old man, unrelated to the petitioner who had no reason to tell lie. Moreover, the husband managed to escape. He never appeared either at the trial court or before this Court to discharge his burden. It was not unknown to him that legal proceedings were initiated by his wife against him because he was arrested in one of the cases instituted by his petitioner wife.

[16] A bare perusal of section 119 of the Evidence Act would show that a deaf and dumb witness who is unable to speak may give his evidence in any other manner intelligible to the court. It may be by writing or by signs in open court. It is evident that the mother [PW-2] and her petitioner daughter [PW-1] came to the court on the same day for giving deposition in the case. It also appears from the record that the petitioner was a literate person. She was able to read and write. Therefore, in case of any doubt, the court could have asked her to communicate her words in writing. The court could have also cleared its doubts from the mother of the petitioner by putting the questions to her in exercise of its power under section 165 of the Evidence Act. Without taking recourse to such means, the Family Court rejected the petition declining to grant maintenance allowance to the petitioner and her daughter which is unacceptable.

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Other Sources :

https://indiankanoon.org/doc/50658253/