05AB1E, 7845 535

Tö

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This converts the input from base 10 according to 05AB1E's codepage. T is mapped to 29 and ö to 245. Digits larger or equal to the base are allowed and "overflow" into the next digit.
This can be inverted by iterating the digits of the output in reverse:

inverse program:

[D0Q#    "loop while TOS != 0"\
T‰`      "divmod 10"\
5Qi      "if the last digit was 10:"\
 'öˆ24-  "append ö to global array and subtract 24 from TOS"\
ë        "else:"\
 'Tˆ2-   "append T to global array and subtrac 2 from TOS"\
]¯RJ     "after the loop: reverse global array and join"\

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05AB1E, 7845 535 34

BC

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This converts the input from base 2 according to 05AB1E's codepage. B is mapped to 11 and C to 12. Digits larger or equal to the base are allowed and "overflow" into the next digit.
This can be inverted by iterating the digits of the output in reverse:

[D0Q#    "loop while TOS != 0"\
2‰`      "divmod 10"\
i        "if the last digit was 1:"\
 'Bˆ5-   "append ö to global array and subtract 5 from TOS"\
ë        "else:"\
 'Cˆ6-   "append T to global array and subtrac 6 from TOS"\
]¯RJ     "after the loop: reverse global array and join"\

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05AB1E, 7845

тö

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This converts the input from base 100 according to 05AB1E's codepage. т is mapped to 76 and ö to 245. Digits larger or equal to the base are allowed and "overflows" into the next digit.
This means that every string of т and ö is interpreted as a base-100 integer with digits 45, 47, 76, 78 and potentially a leading 2.

inverse program:

2K              # remove all 2's
  SιнJ          # get every other digit
      „74„тö‡   # replace 7 with т and 4 with ö

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05AB1E, 7845 535

Tö

Try it online!

This converts the input from base 10 according to 05AB1E's codepage. T is mapped to 29 and ö to 245. Digits larger or equal to the base are allowed and "overflow" into the next digit.
This can be inverted by iterating the digits of the output in reverse:

inverse program:

[D0Q#    "loop while TOS != 0"\
T‰`      "divmod 10"\
5Qi      "if the last digit was 10:"\
 'öˆ24-  "append ö to global array and subtract 24 from TOS"\
ë        "else:"\
 'Tˆ2-   "append T to global array and subtrac 2 from TOS"\
]¯RJ     "after the loop: reverse global array and join"\

Try it online!

05AB1E, 7845

тö

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This converts the input from base 100 according to 05AB1E's codepage. т is mapped to 76 and ö to 245. Digits larger or equal to the base are allowed and "overflows" into the next digit.
This means that every string of т and ö is interpreted as a base-100 integer with digits 45, 47, 76, 78 and potentially a leading 2.

Inverse Program

05AB1E, 7845

тö

Try it online!

This converts the input from base 100 according to 05AB1E's codepage. т is mapped to 76 and ö to 245. Digits larger or equal to the base are allowed and "overflows" into the next digit.
This means that every string of т and ö is interpreted as a base-100 integer with digits 45, 47, 76, 78 and potentially a leading 2.

inverse program:

2K              # remove all 2's
  SιнJ          # get every other digit
      „74„тö‡   # replace 7 with т and 4 with ö

Try it online!