I have just discovered that the data used for the plot on the page https://www.tiobe.com/tiobe-index/fortran/ are hard coded in the source of the page (lines 225-226), in that format (JSON?):
series: [
{name : 'Fortran',data : [[Date.UTC(2001, 5, 30), 1.41], [Date.UTC(2001, 6, 30), 1.31], [Date.UTC(2001, 7, 30), 1.46], [Date.UTC(2001, 8, 28), 1.40], [Date.UTC(2001, 9, 26), 1.32], [Date.UTC(2001, 10, 28), 1.29], [Date.UTC(2001, 11, 31), 1.23], [Date.UTC(2002, 0, 30), 1.23], [Date.UTC(2002, 1, 27), 1.27], [Date.UTC(2002, 2, 29), 1.27], [Date.UTC(2002, 3, 29), 1.28]...
The rank is not included, just the ratings (%). And be careful, I think the months are numbered from 0 to 11! (seems strange as the days are going up to 31…)
In the April index, Fortran is 20th with 0.59%.