6 added 9 characters in body

# Jelly, 13 12 11 bytes

-1 byte thanks to @Luis Mendo (use Ḃ to replace %2)
-1 byte thanks to @Dennis (use a string compression)

Œlf“¡ẎṢɱ»LḂ


All test cases are at TryItOnline

How?

Œlf“¡ẎṢɱ»LḂ - Main link takes an argument - s
Œl          - lowercase(s)
“¡ẎṢɱ»   - string of lowercase vowels (compression using the words a and eoui)
f         - filter - keep only the vowels
L  - length - the number of vowels
Ḃ - Bit (modulo 2)


Non-competing, 5 bytes (since I just added the function Øc)

fØcLḂ


Test cases also at TryItOnline

Same as above, but Øc yields the EnglishLatin alphabet's vowels, 'AEIOUaeiou'

# Jelly, 13 12 11 bytes

-1 byte thanks to @Luis Mendo (use Ḃ to replace %2)
-1 byte thanks to @Dennis (use a string compression)

Œlf“¡ẎṢɱ»LḂ


All test cases are at TryItOnline

How?

Œlf“¡ẎṢɱ»LḂ - Main link takes an argument - s
Œl          - lowercase(s)
“¡ẎṢɱ»   - string of lowercase vowels (compression using the words a and eoui)
f         - filter - keep only the vowels
L  - length - the number of vowels
Ḃ - Bit (modulo 2)


Non-competing, 5 bytes (since I just added the function Øc)

fØcLḂ


Test cases also at TryItOnline

Same as above, but Øc yields the English vowels, 'AEIOUaeiou'

# Jelly, 13 12 11 bytes

-1 byte thanks to @Luis Mendo (use Ḃ to replace %2)
-1 byte thanks to @Dennis (use a string compression)

Œlf“¡ẎṢɱ»LḂ


All test cases are at TryItOnline

How?

Œlf“¡ẎṢɱ»LḂ - Main link takes an argument - s
Œl          - lowercase(s)
“¡ẎṢɱ»   - string of lowercase vowels (compression using the words a and eoui)
f         - filter - keep only the vowels
L  - length - the number of vowels
Ḃ - Bit (modulo 2)


Non-competing, 5 bytes (since I just added the function Øc)

fØcLḂ


Test cases also at TryItOnline

Same as above, but Øc yields the Latin alphabet's vowels, 'AEIOUaeiou'

5 added 98 characters in body

# Jelly, 13 121211bytes

-1 byte thanks to @Luis Mendo (use Ḃ to replace %2)
-1 byte thanks to @Dennis (use a string compression)

Œlf“aeiou”LḂŒlf“¡ẎṢɱ»LḂ


All test cases are at TryItOnlineTryItOnline

How?

Œlf“aeiou”LḂŒlf“¡ẎṢɱ»LḂ - Main link takes an argument - s
Œl           - lowercase(s)
“aeiou”“¡ẎṢɱ»   - string of lowercase vowels (compression using the words a and eoui)
f          - filter - keep only the vowels
L  - length - the number of vowels
Ḃ - Bit (modulo 2)


Non-competing, 5 bytes (since I just added the function Øc)

fØcLḂ


Test cases also at TryItOnline

Same as above, but Øc yields the English vowels, 'AEIOUaeiou'

# Jelly, 1312bytes

-1 byte thanks to @Luis Mendo (use Ḃ to replace %2)

Œlf“aeiou”LḂ


All test cases are at TryItOnline

How?

Œlf“aeiou”LḂ - Main link takes an argument - s
Œl           - lowercase(s)
“aeiou”   - string of lowercase vowels
f          - filter - keep only the vowels
L  - length - the number of vowels
Ḃ - Bit (modulo 2)


Non-competing, 5 bytes (since I just added the function Øc)

fØcLḂ


Test cases also at TryItOnline

Same as above, but Øc yields the English vowels, 'AEIOUaeiou'

# Jelly, 13 1211bytes

-1 byte thanks to @Luis Mendo (use Ḃ to replace %2)
-1 byte thanks to @Dennis (use a string compression)

Œlf“¡ẎṢɱ»LḂ


All test cases are at TryItOnline

How?

Œlf“¡ẎṢɱ»LḂ - Main link takes an argument - s
Œl          - lowercase(s)
“¡ẎṢɱ»   - string of lowercase vowels (compression using the words a and eoui)
f         - filter - keep only the vowels
L  - length - the number of vowels
Ḃ - Bit (modulo 2)


Non-competing, 5 bytes (since I just added the function Øc)

fØcLḂ


Test cases also at TryItOnline

Same as above, but Øc yields the English vowels, 'AEIOUaeiou'

4 added 69 characters in body

# Jelly, 1313 12bytes

-1 byte thanks to @Luis Mendo (use Ḃ to replace %2)

Œlf“aeiou”L%2Œlf“aeiou”LḂ


All test cases are at TryItOnlineTryItOnline

How?

Œlf“aeiou”L%2Œlf“aeiou”LḂ - Main link takes an argument - s
Œl            - lowercase(s)
“aeiou”    - string of lowercase vowels
f           - filter - keep only the vowels
L   - length - the number of vowels
%2Ḃ - Bit (modulo 2)


Non-competing, 65 bytes (since I just added the function Øc)

fØcL%2fØcLḂ


Test cases also at TryItOnlineTryItOnline

Same as above, but Øc yields the English vowels, 'AEIOUaeiou'

# Jelly, 13bytes

Œlf“aeiou”L%2


All test cases are at TryItOnline

How?

Œlf“aeiou”L%2 - Main link takes an argument - s
Œl            - lowercase(s)
“aeiou”    - string of lowercase vowels
f           - filter - keep only the vowels
L   - length - the number of vowels
%2 - modulo 2


Non-competing, 6 bytes (since I just added the function Øc)

fØcL%2


Test cases also at TryItOnline

Same as above, but Øc yields the English vowels, 'AEIOUaeiou'

# Jelly, 13 12bytes

-1 byte thanks to @Luis Mendo (use Ḃ to replace %2)

Œlf“aeiou”LḂ


All test cases are at TryItOnline

How?

Œlf“aeiou”LḂ - Main link takes an argument - s
Œl           - lowercase(s)
“aeiou”   - string of lowercase vowels
f          - filter - keep only the vowels
L  - length - the number of vowels
Ḃ - Bit (modulo 2)


Non-competing, 5 bytes (since I just added the function Øc)

fØcLḂ


Test cases also at TryItOnline

Same as above, but Øc yields the English vowels, 'AEIOUaeiou'

3 added 336 characters in body
2 added 406 characters in body
1