'however slow' is correct and can be used in written English.
It is usually used to express contrast or an unexpected situation. For example, "He normally runs short distances quickly, however slow he did today."
"There are definitely signs of rebirth, however slow.
It can, however, slow the growth of the tumour.
The recovery, however slow and painful, he says, cannot be hurried.
"However slow the economy, or chaotic the markets, our checks will clear," he said.
Until now the journey along that road, however slow, has always been in the right direction.
But however slow the nation's economic recovery might be, he said, he predicts substantial growth for Fidelis.
She declares, "Without a revolution of the inner life, however slow, all our big designs are worthless".
That, combined with G.E.'s decision to hand back his money, marks progress, however slow and grinding it may feel.
But however slow the market is now, compared with the one that Mr. Occhipinti first knew some 25 years ago, Pomona's values have soared.
They also, however, slow the absorption of nutrients when a seed eventually finds soil that is good enough to grow in.
The one area in which the Egyptians welcomed Israeli interest was agriculture.A senior Israeli official, heroically optimistic, insists that progress, however slow, is discernible beneath the surface.
