I am transcribing a grade 5 Spanish book for Mexican students.Please advise me how to transcribe the following native languages (see attachment) which contain accented letters that are not specified in the Spanish/Mexican braille alphabets.
Thank you for the interesting question. Can you clarify: Is this a textbook being used by Spanish-speaking students in Mexico? If so, according to Method 4 of BANA's Provisional Guidance for Transcribing Foreign Language Material in UEB, you would most likely transcribe it using the full braille code in use in Mexico, in which case I would not be able to advise you on the specifics.
According to World Braille Usage (page 93), the governing bodies for literary braille standards in Mexico are:
Latin American Braille Council [Comisión Braille Latinoamericana] (CBL)
It might be worth trying to contact someone at one of those agencies to see if there are published braille alphabets used in Mexico for the indigenous languages.
If the student is expected to be familiar with Unified English Braille conventions and symbols, then the only alternative I can think of is to use the Modifiers provided in UEB 4.2 to indicate to the student which type of accents/modifiers are used on the letters (acute, breve, solidus overlay, etc.). This would not be using the foreign accented characters normally used in those languages, but would at least allow the student to read the words in some form. Skimming through your print example (thank you for that!), it looks like there are a few modifiers which are not in the list in 4.2, so you would have to use the transcriber-defined modifiers for those and let the student know what they mean on the Special Symbols page (for example, ^_1 could be used to represent "bar under following letter" for the two letter a's in the first phrase).