It only happened recently, maybe four years ago, that I started liking the language of my adopted country - English. Before that time I spent nearly 20 years in the US hating the language. Well - English is hard to learn, hard to pronounce, has a voluminous dictionary of words borrowed from all over and is full of idiosyncratic usage. Foreigners have trouble with all those elements.
Hard to pronounce - large set of vowel sounds and very specific articulation of many consonants make the phonetics a large part of the learning process. Foreigners have to make an enormous effort to control their speaking habits in order to approximate English sounds reasonably. Americans for that matter have trouble speaking standard English and love retaining their regional (Southern, New York, etc) speaking habits. Additionally, native English speakers have trouble learning other common world languages.
The large volume of adopted vocabulary - I think above 500k of words - is more than twice as large as the standard French dictionary. This is due to voracious adoption of foreign words that are used to designate very specific objects - for example seller, vendor or merchant - are really all synonyms but practice assigns them very specific differing semantics.
This leads to the problem of idiosyncratic usage. Words appearing as synonyms cannot be substituted one for another - they function correctly only in their environment designed by the intractable minds of native speakers. For example: airtime - functions correctly only when referring to mobile phone usage although it could mean a variety of things.
All those factors make English very hard to learn by non-native speakers and really a poor candidate for a lingua franca of the world which it has unfortunately become. There must be something else that propelled this language toward this function. I don't know what but its career is similar to that of Microsoft operating software known as Windows. Programming for that system is also full of inconsistencies and idiosyncrasies and forces one to guess around badly formulated paradigms that fail to express what the system does. Nevertheless that operating system and programming for it has become a dominant aspect of software usage in much of the world. Grappling with semantics filled with specificity and failing to plainly express the logical structure of concepts and operations has now become a fate of all of us.
Of course those who are native English speakers have the upper hand - just like those laptop computers where Windows is already preinstalled and preconfigured. There will be surprises and unpleasant discoveries but having English preinstalled in your head by your mother and your organs of speech pretrained gets you certain commercial advantages - like being an English tutor for those of us where the symbolic system does not run with native smoothness. Additionally a certain aristocratic aura surrounding the native English speaker tends to draw attention away from cultural and intellectual contributions expressed in other languages. It puts the center of the world in the US and British Isles.