Sets and slices

VOWELS = {"a", "e", "i", "o", "u"}
VOWELS_Y = {"a", "e", "i", "o", "u", "y"}
SPECIALS = {"xr", "yt"}


def translate(text):
    piggyfied = []

    for word in text.split():
        if word[0] in VOWELS or word[0:2] in SPECIALS:
            piggyfied.append(word + "ay")
            continue

        for pos in range(1, len(word)):
            if word[pos] in VOWELS_Y:
                pos += 1 if word[pos] == 'u' and word[pos - 1] == "q" else 0
                piggyfied.append(word[pos:] + word[:pos] + "ay")
                break

    return " ".join(piggyfied)

This approach begins by defining sets for looking up matching characters from the input. Python doesn't enforce having real constant values, but the sets are defined with all uppercase letters, which is the naming convention for a Python constant. It indicates that the value is not intended to be changed.

The translate() function begins by defining the list which will hold the parsed value(s).

The input is split() into a list of its words, which is then iterated.

String indexing is used to check if the first letter of the word is in the set of vowels. If so, the logical or operator "short-circuits" and the word plus "ay" is appended to the list. If the first letter is not a vowel, then a slice of the first two letters is used to check if they match any of the special beginning characters. If the letters match, the word plus "ay" will be appended to the list. If the beginning of the word matches either condition, the loop continues to the next word.

If the beginning of the word did not match either condition, that leaves ranging its characters from position 1 until the len() of the word.

The inner loop iterating characters is nested within the outer loop that iterates the words. Each character is iterated until finding a vowel (at this point, the letter y is now considered a vowel.) If the vowel is u, the previous consonant is checked to be q. If so, the position is advanced to be one position after the found u.

A slice is then taken from the position until the end of the word, plus a slice taken from the beginning of the word and stopped just before the position, plus ay. That concatenated string is appended to the list, break is called to exit the inner loop, and execution returns to the outer loop.

Once all of the words in the input have been iterated, the join method is called on a space character to connect all of the words in the list back into a single string. Since the space is only used as a separator between elements of the list, if the list has only one element, the space will not be added to the beginning or end of the output string.