(This isn’t for your benefit, your know this already, but for
@maniak)
In Russian -o is pronounced as -a when the vowel is not in the stressed syllable.
For example the word хорошо (meaning ”good”) is made up of 3 syllables (хо-ро-шо). In this case it is the last syllable that is stressed (шо). The English transliteration would be kharashO (uppercase to show the stressed vowel). The first two -o are pronounced as -a. Because they are not stressed.
By this rule the name Лукашенко is prounounced LukashEnka in Russian (stress on the E). In Belarusian things are more simplified. Where they pronounce -a they also write -a. So the name is written as Лукашенка in Belarusian.
In both Russian and Belarusian it’s pronounced the same, with -a at the end. But since in Russian it’s written with an -o at the end, sometimes people write it as Lukashenko in English. But closest correct pronunciation is Lukashenka.