Ultimately a law degree is a fantastic tool for employment after uni. It is considered a generalist degree now, and is admired in various employment fields including the traditional path of law school to solicitor, as well as public service including diplomacy or business. Over 50% of law students don't become lawyers by being admitted after uni; many law students know they won't practice law.
The law firms claim they do not care whether you do an arts/law degree or a commerce law degree, however in an interview for a clerkship they may ask you why you are applying to a commercial firm with zero awareness which you can counter by stating law exposes you to commerce and just like commerce graduates you are inexperienced etc Alternatively, you could stress you love languages and thus wanted to do an arts degree to continue that passion. Whatever the case, so long as you have good marks its shouldn't matter in the law firm situation.
Further my friend who has graduated is working in one of the big 4 accountancy firms in the tax law department. This friend did arts/law with a major in politics. After 2 years if he wishes to continue working in the tax department he can to do a CA (Chartered Accountancy course) otherwise he moves to a different area (precisely what - I cannot recall). Regardless, a law degree in itself can get you into business.
That being said commerce is good as it gives you are grounding in business related things - but be warned - there are degrees of commerce subjects from management or marketing ('soft commerce') to economics to actuarial studies. Commerce in itself now is very broad.But be warned, heaps of people hate the commerce side who do law with me.
If you prefer humanities then arts is a better move. I have found that arts/law kids generally go well in law exams because of their ability to write well. I initially wondered whether it was a bad move, but on reflection I am very happy with my choice of not doing commerce and I am very much enjoying studying law.