They are/can be 'logic' terms. A unless B means A only happens if B doesn't happen. A as long as B mean A only happens while B is true. Usually - unless is used with a negative verb. So - You can't eat your pudding unless you eat your meat. ( if you want pudding you have to eat your meat ) I won't go unless you come too. ( I will only go if you go) As long as - is used to show a potential end to a situation, or that agreement is needed. I will stay up as long as the cartoons are on TV. I will wash the dishes as long as you dry them. I will answer your iTalki question as long as you give me a 'best answer' tick.

1. Learners will never speak English fluently UNLESS they completely understand the difference between the verb "to be" and all other verbs. / UNLESS learners completely understand the difference between the verb "to be" and all other verbs, they will never speak English fluently. 2. Learners will never speak English fluently AS LONG AS they fail to completely understand the difference between the verb "to be" and all other verbs. / AS LONG AS learners fail to completely understand the difference between the verb "to be" and all other verbs, they will never speak English fluently.

unless is being used as a condition to comply something . but as long as can be used in continuation that this will goes on as long as that is happening.