In one of the loading screens the game states that the cities have a maximum level of 10, but in the game you can not grow a city beyond level 9.

Literal text from CoreFlavorText.xml:

Cities gain levels based on the amount of Food available to grow their population. There are ten different levels, each unlocking unique buildings to construct.

Either the text or the implemented city maximum is wrong. 

Please let it the error be the implemented city maximum, because then when it is corrected i will be able to grow my cities another level.

PS:

Speaking of city levels: It is very hard to see which tiles have been claimed and which are not (during a city upgrade).

And the tile yields are sometimes misaligned (showing on a tile above the tile they belong to) unless you zoom out.