Who sang lazy hazy crazy days of summer?
No context provided
Who sang lazy hazy crazy days of summer in German?
Willy Hagara
No context provided
Who sang lazy hazy crazy days of summer in English?
Nat King Cole Nathaniel Adams Coles
Those Lazy-Hazy-Crazy Days
https://en.wikipedia.org/wiki/Those%20Lazy-Hazy-Crazy%20Days
Nat King Cole
https://en.wikipedia.org/wiki/Nat%20King%20Cole
"Those Lazy-Hazy-Crazy Days of Summer" is a popular song composed by Hans Carste. It was originally written as "Du spielst 'ne tolle Rolle", with German lyrics by Hans Bradtke (de), and was first recorded under that title in 1962 by Willy Hagara.[1]

In 1963, it was recorded by Nat King Cole, with English lyrics written by Charles Tobias on a theme of nostalgia.
Those Lazy-Hazy-Crazy Days of Summer (song)
Hans Friedrich August Carste (5 September 1909 in Frankenthal – 11 May 1971 in Bad Wiessee) was a German composer and conductor.
Hans Carste
Willy Hagara (4 June 1927 – 15 May 2015) was an Austrian schlager pop singer and actor.
Willy Hagara
Cole had one of his last major hits in 1963, two years before his death, with "Those Lazy-Hazy-Crazy Days of Summer", which reached number 6 on the Pop chart.
Nat King Cole
There were multiple recordings of Those Lazy-Hazy-Crazy Days of Summer, including the original German version by Willy Hagara and an English recording by Nat King Cole. Those Lazy-Hazy-Crazy Days of Summer was composed by Hans Carste, a German composer and conductor, with German lyrics by Hans Bradtke. It was first recorded in 1962 by Willy Hagara, an Austrian pop singer and actor, who sang the song in German. It was recorded in 1963 by Nat King Cole, an American singer, jazz pianist, and actor, with English lyrics written by Charles Tobias, one of Cole's last major hits.