Dividends will always have your marginal Irish income tax rate applied.
You could also end up paying a portion of the foreign government tax on top of this if you don't make a foreign tax reclaim.
In the example I gave you could pay 40% Irish tax and 10% foreign tax.
Here's a concrete example from my modest investment in SAP based on the 2023 dividend
Number of shares
80
Dividend per share
€ 2.05
Gross dividend
€ 164.00
German withholding tax (25% + 5.5% solidarity surcharge of tax)
€ 43.26
Net dividend received in my brokerage account
€ 120.74
Irish tax return (Form 11)
Gross dividend
€ 164.00
Tax due at marginal rate (40% in my case)
€ 65.60
Credit for German withholding tax as per double taxation treaty 15%
€ 24.60
Irish tax due
€41.00
Tax deducted on behalf of German Tax authority
€ 43.26
Maximum tax allowed by double taxation treaty 15%
€ 24.60
Tax reclaimable from German Tax Authority
€ 18.66
However, I can't be bothered with all the paper work to reclaim the € 18.66 - but if it was a more significant amount, I certainly would even given the long delays reported