[squirt]

Easy.

  declare -A outer=(
    [inner]="_inner"
  )
  declare -A _inner=(
    [key]="value"
  )

Access inner elements via a nameref.

  declare -n inner="${outer[inner]}"
  echo "${inner[key]}"
  # value

Currently writing a compiler in Bash built largely on this premise.

[kotlin2]

That seems really inconvenient to be honest.