I came across a UNESCO statistics page that reveals the number of authors' works translated into other languages. If ever there was a statistic that most clearly demonstrates worldwide popularity over time this must be it. There are a few recognised SFF authors on the list (which I have highlighted in a nice blue colour). Verne comes in second, which rather surprised me, though I had heard Christie was top so was not surprised by that. I was impressed to see that Asimov (24th) has had his work translated into more volumes than Dickens, Hemingway, Balzac (and Tolkien)! There's not an awful lot to say about the list perhaps, but i thought Chrons folk might be mildly interested.
1 Christie Agatha 7233
2 Verne Jules 4751
3 Shakespeare William 4281
4 Blyton Enid 3921
5 Cartland Barbara 3648
6 Steel Danielle 3628
7 Lenin Vladimir Il'ič 3592
8 Andersen Hans Christian 3520
9 King Stephen 3354
10 Grimm Jacob 2976
11 Grimm Wilhelm 2950
12 Roberts Nora 2597
13 Dumas Alexandre 2540
14 Doyle Arthur Conan 2495
15 Twain Mark 2428
16 Dostoevskij Fedor Mihajlovič 2340
17 Simenon Georges 2315
18 Lindgren Astrid 2270
19 Joannes Paulus II 2257
20 Goscinny René 2234
21 Stine Robert L. 2221
22 London Jack 2181
23 Tolstoj Lev Nikolaevič 2178
24 Asimov Isaac 2158
25 Dickens Charles 2107
26 Stevenson Robert Louis 2039
27 Steiner Rudolf 1868
28 Wilde Oscar 1787
29 Sheldon Sidney 1732
30 Holt Victoria 1660
31 Marx Karl 1643
32 Balzac Honoré de 1590
33 Hemingway Ernest 1569
34 Ludlum Robert 1530
35 Hesse Hermann 1521
36 Kafka Franz 1491
37 Koontz Dean R. 1491
38 Nietzsche Friedrich Wilhelm 1490
39 Rajanīśa 1488
40 Clark Mary Higgins 1485
41 Platon 1479
42 Čehov Anton Pavlovič 1473
43 Tolkien John Ronald Reuel 1458
44 Poe Edgar Allan 1435
45 Kipling Rudyard 1424
46 Perrault Charles 1401
47 Dahl Roald 1398
48 Goethe Johann Wolfgang von 1397
49 García Márquez Gabriel 1395
1 Christie Agatha 7233
2 Verne Jules 4751
3 Shakespeare William 4281
4 Blyton Enid 3921
5 Cartland Barbara 3648
6 Steel Danielle 3628
7 Lenin Vladimir Il'ič 3592
8 Andersen Hans Christian 3520
9 King Stephen 3354
10 Grimm Jacob 2976
11 Grimm Wilhelm 2950
12 Roberts Nora 2597
13 Dumas Alexandre 2540
14 Doyle Arthur Conan 2495
15 Twain Mark 2428
16 Dostoevskij Fedor Mihajlovič 2340
17 Simenon Georges 2315
18 Lindgren Astrid 2270
19 Joannes Paulus II 2257
20 Goscinny René 2234
21 Stine Robert L. 2221
22 London Jack 2181
23 Tolstoj Lev Nikolaevič 2178
24 Asimov Isaac 2158
25 Dickens Charles 2107
26 Stevenson Robert Louis 2039
27 Steiner Rudolf 1868
28 Wilde Oscar 1787
29 Sheldon Sidney 1732
30 Holt Victoria 1660
31 Marx Karl 1643
32 Balzac Honoré de 1590
33 Hemingway Ernest 1569
34 Ludlum Robert 1530
35 Hesse Hermann 1521
36 Kafka Franz 1491
37 Koontz Dean R. 1491
38 Nietzsche Friedrich Wilhelm 1490
39 Rajanīśa 1488
40 Clark Mary Higgins 1485
41 Platon 1479
42 Čehov Anton Pavlovič 1473
43 Tolkien John Ronald Reuel 1458
44 Poe Edgar Allan 1435
45 Kipling Rudyard 1424
46 Perrault Charles 1401
47 Dahl Roald 1398
48 Goethe Johann Wolfgang von 1397
49 García Márquez Gabriel 1395